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

[vamshin]

This plugin is supposed to be release its first version from 2.1.0. Closing this and keep track of separate issue

[zelinh]

Since this plugin have been released within the bundle for some times, we should be starting to add BWC tests for this plugin for plugin level and eventually on distribution bundle level as well.
See here for more info on distribution level BWC tests.

[zelinh]

Adding 2.10.0 label here.

[zelinh]

Can we get some traction on this issue? This BWC tests request would be a future release blocker.

[zelinh]

@vamshin Do we have a plan to onboard these BWC tests? We are planning to add BWC tests as mandatory exit criteria in future releases as we are seeing more number of BWC test failures during releases.