v1/topdown/graphql: Cache GraphQL schema parse results (open-policy-agent#5377)

This commit stores parsed GraphQL schemas to the cache, which improves
the performance of GraphQL operations that parse the schema more than once.

Queries are not cached.

pkg: github.com/open-policy-agent/opa/v1/topdown
cpu: Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
BenchmarkGraphQLSchemaIsValid/Trivial_Schema_-_string-16	                   15519            100178 ns/op
BenchmarkGraphQLSchemaIsValid/Trivial_Schema_with_cache_-_string-16               371311              3383 ns/op
BenchmarkGraphQLSchemaIsValid/Trivial_Schema_with_cache_-_AST_object-16            66594             18093 ns/op
BenchmarkGraphQLParseSchema/Trivial_Schema_-_string-16                              6429            173773 ns/op
BenchmarkGraphQLParseSchema/Trivial_Schema_with_cache_-_string-16                   6523            170819 ns/op
BenchmarkGraphQLParseQuery/Trivial_Query_-_string-16                               16352             72777 ns/op
BenchmarkGraphQLParseQuery/Trivial_Query_with_cache_-_string-16                    16083             73548 ns/op
BenchmarkGraphQLIsValid/Trivial_Schema_-_string-16                                 14320             83589 ns/op
BenchmarkGraphQLIsValid/Trivial_Schema_with_cache_-_string-16                      71486             15463 ns/op
BenchmarkGraphQLParse/Trivial_Schema_-_string-16                                    3380            321490 ns/op
BenchmarkGraphQLParse/Trivial_Schema_with_cache_-_string-16                        13909             87633 ns/op
BenchmarkGraphQLParseAndVerify/Trivial_Schema_-_string-16                           3435            327646 ns/op
BenchmarkGraphQLParseAndVerify/Trivial_Schema_with_cache_-_string-16               13844             85213 ns/op
PASS
ok      github.com/open-policy-agent/opa/v1/topdown     112.465s

Resolves: open-policy-agent#5377

Signed-off-by: Rob Myers <[email protected]>

Author: robmyersrobmyers

Diff for: docs/content/configuration.md

@@ -863,14 +863,15 @@ Caching represents the configuration of the inter-query cache that built-in func
 functions provided by OPA, `http.send` is currently the only one to utilize the inter-query cache. See the documentation
 on the [http.send built-in function](../policy-reference/#http) for information about the available caching options.
 
-It also represents the configuration of the inter-query _value_ cache that built-in functions can utilize. Currently, 
+It also represents the configuration of the inter-query _value_ cache that built-in functions can utilize. Currently,
 this cache is utilized by the `regex` and `glob` built-in functions for compiled regex and glob match patterns
-respectively, and the `json.schema_match` built-in function for compiled JSON schemas.
+respectively, the `json.schema_match` built-in function for compiled JSON schemas, and any `graphql` built-in function
+that requires GraphQL schemas.
 
 | Field                                                                    | Type    | Required | Description                                                                                                                                                                                                                                          |
 |--------------------------------------------------------------------------|---------|----------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | `caching.inter_query_builtin_cache.max_size_bytes`                       | `int64` | No       | Inter-query cache size limit in bytes. OPA will drop old items from the cache if this limit is exceeded. By default, no limit is set.                                                                                                                |
-| `caching.inter_query_builtin_cache.forced_eviction_threshold_percentage` | `int64` | No       | Threshold limit configured as percentage of `caching.inter_query_builtin_cache.max_size_bytes`, when exceeded OPA will start dropping old items permaturely. By default, set to `100`.                                                               |
+| `caching.inter_query_builtin_cache.forced_eviction_threshold_percentage` | `int64` | No       | Threshold limit configured as percentage of `caching.inter_query_builtin_cache.max_size_bytes`, when exceeded OPA will start dropping old items prematurely. By default, set to `100`.                                                               |
 | `caching.inter_query_builtin_cache.stale_entry_eviction_period_seconds`  | `int64` | No       | Stale entry eviction period in seconds. OPA will drop expired items from the cache every `stale_entry_eviction_period_seconds`. By default, set to `0` indicating stale entry eviction is disabled.                                                  |
 | `caching.inter_query_builtin_value_cache.max_num_entries`                | `int`   | No       | Maximum number of entries in the Inter-query value cache. OPA will drop random items from the cache if this limit is exceeded. By default, set to `0` indicating unlimited size.                                                                     |
 | `caching.inter_query_builtin_value_cache.named.io_jwt.max_num_entries`   | `int`   | No       | Maximum number of entries in the `io_jwt` cache, used by the [`io.jwt` token verification](../policy-reference/#tokens) built-in functions. OPA will drop random items from the cache if this limit is exceeded. By default, this cache is disabled. |