[CI] Removing 2.4 and 2.5 tests in CI

Minor updates

Updates README files

renamed docker image name in README

Fix missing environment dependency for import tasks

Template installs deps using main branch

[DOCS] Updates README and links to elasticsearch-dsl

Bumps version to 7.2.1

[DOCS] Updates README

[DOCS] Updates CHANGELOG for 7.2.1

[CI] Updates JRuby version in GitHub Actions

Renames master to main

update method missing for Ruby 2.x-3.0 all at once

use respond_to_missing? not respond_to?

fix proxying keyword arguments