Pubtools-quay

* Disable sending UMB messages for taggign and untagging images

* Use SSL certificates for Pyxis authentication
* Remove duplicate digests when getting signatures from Pyxis
* Remove return of push_docker entrypoint

* Don't raise 404 errors when deleting tags during rollback

* Fix installation of 'docker' dependency on Python 2.6

* Add hooks to declare events of interest
* Create documentation
* Add option to execute commands inside a container
* Add pagination support for getting all tags via Docker HTTP API
* Capture IIB operation exception
* Get index image manifests with its own token
* Lower python-qpid-proton version

* Create entrypoint for removing a Quay repo
* Create entrypoint for clearing a Quay repo
* Add signature removal to tag-docker operations
* Drop unnecessary 'external_repos'
* Add using extra Quay tokens for OSBS organizations
* Allow specifying multiple repos in remove-repo and clear-repo tasks
* Skip signing when no operator claim messages are constructed
* Add support for delimeter-less repositories
* Change "repo" parameter of claim messages to have external representation
* Fix loggers per pubtools conventions
* Check username in output of skopeo --get-login
* Remove the usage of Quay API reading repo data
* Add signature removal for IIB operations
* Update sigstore to be up-to-date with current implementation
* Allow pushing to non-existent repo