Document the removal of chunk cache for users and operators in the WiredTiger release notes.

The release notes should cover:

• Chunk cache is removed as of this version
• Configuration keys chunk_cache.* are no longer valid and will cause an error if passed
• WiredTigerCC.wt files from previous versions are ignored on open
• Recommended migration path for users who had chunk cache enabled

Acceptance criteria: release notes reviewed and merged alongside final develop merge.