ActiveContext indexer for elasticsearch

gems/gitlab-active-context/.rubocop.yml

gems/gitlab-active-context/README.md

...itlab-active-context/lib/active_context/bulk_processor.rb

...-context/lib/active_context/databases/concerns/adapter.rb

...-context/lib/active_context/databases/concerns/indexer.rb

...ext/lib/active_context/databases/elasticsearch/adapter.rb

...text/lib/active_context/databases/elasticsearch/client.rb

...ext/lib/active_context/databases/elasticsearch/indexer.rb

...ontext/lib/active_context/databases/opensearch/adapter.rb

...ontext/lib/active_context/databases/opensearch/indexer.rb

...ontext/lib/active_context/databases/postgresql/adapter.rb

...ontext/lib/active_context/databases/postgresql/indexer.rb

...ve-context/spec/lib/active_context/bulk_processor_spec.rb

...ib/active_context/databases/elasticsearch/indexer_spec.rb

gems/gitlab-active-context/spec/spec_helper.rb