feat: server side support for authorized retrievals

[alanshaw]

This PR add server side support for authorized retrievals. This involves 2 different authorized retrieval types:

1. Users can send a delegation for retrieving data from a space (per feat: client support for authorized retrievals #249) and it will now be used by the indexer to make a UCAN authorized retrieval (space/content/retrieve) from the relevant node (if not cached).
2. When an upload service invokes assert/index, the indexer will now obtain a service delegation from the node that is storing the index (using access/grant) before making a UCAN authorized retrieval (blob/retrieve) to obtain the index. See rfc: on-demand service authorization RFC#68 for details of on-demand service retrievals.

TODO: a test for (2)

[codecov]

Codecov Report

❌ Patch coverage is 39.41909% with 146 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/service/service.go	37.60%	67 Missing and 11 partials ⚠️
pkg/service/blobindexlookup/simplelookup.go	50.79%	22 Missing and 9 partials ⚠️
cmd/query.go	0.00%	11 Missing ⚠️
pkg/types/types.go	15.38%	11 Missing ⚠️
pkg/construct/construct.go	0.00%	9 Missing ⚠️
pkg/server/server.go	66.66%	4 Missing and 2 partials ⚠️

Files with missing lines	Coverage Δ
pkg/service/blobindexlookup/cachinglookup.go	100.00% <100.00%> (ø)
pkg/server/server.go	38.66% <66.66%> (+1.41%)	⬆️
pkg/construct/construct.go	0.00% <0.00%> (ø)
cmd/query.go	0.00% <0.00%> (ø)
pkg/types/types.go	66.66% <15.38%> (-25.65%)	⬇️
pkg/service/blobindexlookup/simplelookup.go	53.75% <50.79%> (-21.25%)	⬇️
pkg/service/service.go	70.80% <37.60%> (-10.03%)	⬇️

... and 1 file with indirect coverage changes

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