Addition of support of async metadata extraction via T-Engines.
Still needs support for RM to control what is extracted in emails.
Still includes OOTB metadata extractors. To be removed.
Still needs removal of legacy transformers and 3rd party libraries they use.
Merge branch 'feature/REPO-4334_metadata' into feature/repo-4334_XXXX so that we have a single commit to cherry pick into the new projects.
(cherry picked from commit 18f0e9c8b1a4df33a5fa303e5fd21e5fdb1fd4bd)