server: Add feature flags that helps TiKV to implement feature gate that doesn't depend on incremental semver

[MyonKeminta]

What problem does this PR solve?

Issue Number: Close #xxx

• Requires Add feature_flags field to PutStoreRequest and StoreHeartbeatResponse pingcap/kvproto#1396

What is changed and how does it work?

Adds support for receiving feature flags from TiKV and send cluster feature flags via StoreHeartbeatResponse. This makes it possible for TiKV to implement a feature gate without depending on incremental semver.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

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