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

The tests have been added for the upgrade path of 1.13.0.0 to 1.1.0.0 plugin version with respective OpenSearch versions.
PRs:

1. Adding mixed cluster, rolling upgrade, restart upgrade bwc tests #158
2. Add bwc tests to run with CI #181
3. Adding a task for running bwc tests combined #185

This issue is for adding tests for other upgrade paths for various versions and adding assertions for all the features.

[ylwu-amzn]

BWC added