[Spark] Resolve inconsistencies between the V2 Checkpoint specification and implementation

[dhruvarya-db]

Which Delta project/connector is this regarding?

• Spark
• Standalone
• Flink
• Kernel
• Other (fill in here)

Description

Follow-up for #2214.

The V2 Checkpoint implementation does not match with what is expected in the PROTOCOL in some places.
It does not write some fields in the V2 Checkpoint-related actions:

1. flavor in checkpointMetadata
2. type in sidecar
   Also,
3. The implementation writes a field called version (checkpoint version) in checkpointMetadata and relies on it but the PROTOCOL does not specify any such fields.
4. The PROTOCOL requires that the sidecar’s relative file path should be specified under the field fileName in the sidecar action. But the implementation writes this under the field name path.

This PR updates the specification so that it correctly reflects the implementation.

Does this PR introduce any user-facing changes?

No