Document and verify schema migration operations support matrix

[coderabbitai]

Context

This issue tracks the need to explore, document, and verify which Fivetran schema migration operations are supported by CrateDB and how unsupported operations are handled.

Background

During review of PR #107, the question arose: Can Fivetran emit schema migration operations that CrateDB doesn't support, and if so, how should they be handled?

The current 0.0.x implementation focuses on satisfying the Fivetran SDK tester test cases without comprehensive analysis of all possible operations.

Tasks

• Explore the complete surface of possible schema migration operations that Fivetran can emit
• Match these operations against CrateDB's capabilities
• Identify gaps between Fivetran operations and CrateDB support
• Document which operations are supported vs. unsupported
• Document how unsupported operations are currently handled (or should be handled)
• Create user-facing documentation to clarify supported operations

References

• PR Schema migrations: Template file blueprints and minimal CrateDB implementation #107: Schema migrations: Template file blueprints and minimal CrateDB implementation #107
• Fivetran Partner SDK: https://github.com/fivetran/fivetran_partner_sdk
• Related: SDK feature: Schema migrations #86

Requested by

@amotl in #107