Spec: Add implementation note for determining manifest list format version

[yshcz]

Closes #14926.

While implementing the spec, I looked into how other implementations detect the format version of manifest list files and found some notable differences in approaches:

Implementation	Description
Java	Uses Avro schema resolution without version-specific read path - always uses the same schema that includes all fields up to V3+
Python	Similar to Java - uses schema resolution with a fixed read schema
Rust	Uses current version of table metadata and branches on it, though a TODO comment notes this may not be needed
Go	Reads format-version from Avro metadata and errors if missing, which is not strictly following the spec since this field is not required for manifest lists

This PR adds an implementation note to Appendix F to document the recommended approach and guide future implementations. It explains how Avro schema resolution enables implementations to use a single read schema without version detection, how to determine the exact format version when needed (by examining the writer schema), and why format-version in Avro metadata cannot be reliably used for manifest lists.

If manifest lists are removed in v4, this note would only apply to v1 to v3. I'm not sure how to frame this, any guidance from reviewers would be appreciated.