KAFKA-20328 : Part 1 - headers-aware api test coverage

[muralibasani]

Ref : https://issues.apache.org/jira/browse/KAFKA-20328

After audit, found a few gaps and also considered the work of 1271 kip
This is first PR. Next PRs will be on Decorator/forwarder coverage — AbstractReadWriteDecorator and AbstractReadX related and other integration tests

This PR :

• new tests for PlainToHeadersWindowStoreIteratorAdapterTest, RocksDBMigratingWindowStoreWithHeaders and TimestampedToHeadersStoreAdapter (considered deleted files in KAFKA-20224: Refactor Streams iterator adapters to reduce duplication #21830)
• Update StoresTest with coverage for all 6 *WithHeaders factory methods on Stores
• New test : DslStoreFormatTest cases for HEADERS enum
• New contract tests for TimestampedKeyValueStoreWithHeaders, TimestampedWindowStoreWithHeaders and SessionStoreWithHeaders (with put, get, range, fetch, and backwardFetch, etc)

[muralibasani]

@aliehsaeedii pls take a look.
Considered the comments from the previous pr.