Add backwards compatibility tests for automation

[VachaShah]

Add backwards compatibility tests for the plugin to automate end-to-end upgrade paths for faster releases. Developer documentation for implementing bwc tests and hooking them to CI: https://github.com/opensearch-project/opensearch-plugins/blob/main/TESTING.md#backwards-compatibility-testing

[kkhatua]

Perftop will be on a deprecation path while we work towards creating a Dashboard-based equivalent.