Create a MIGRATION.md

[jpower432]

Objective

Now that the v1.0.0 breaking changes have been merged, we need a MIGRATION.md to help our users transition their existing catalogis and SDK implementations.

Completion Criteria

The MIGRATION.md must include the following sections:

• High-Level Summary
• Schema Mapping (CUE):
  • Rename Table (e.g., family → group).
  • Structural changes (moving fields into and out of metadata blocks).

Known Breaking Changes

#299
#312
#320
#239
#247
#230
#359

[jpower432]

cc @Satarupa22-SD is working on this