Improve the time taken by Github Actions on pull requests

[VachaShah]

Coming from opensearch-project/opensearch-clients#53, update the workflows to reduce the amount of time taken by Github actions for integration tests.

[Yury-Fridlyand]

• Cache plugin build for existing integration tests (low impact, high benefit). See example: https://github.com/opensearch-project/opensearch-dsl-py/blob/2b9e688aa314098956fe7b7bd47618fc10340182/.github/workflows/integration-unreleased.yml#L31-L48
• Cache entire OpenSearch build (very low benefit)
• Use OpenSearch docker container (very low benefit)
• Run integration tests in parallel on all cluster types (low impact, high benefit)
• Add cache save-restore before and after cluster configuration procedure (high impact, low benefit) - need to do big changes in the test framework
• Add integration tests on unreleased versions and use cache as shown in p1

[VachaShah]

Looks like this is already done for this repo.