Add Docker image artifact URL to PR comment (#23484)

* added get_tar_url method

added uts for post message

mv urls to consts

* added notify main uts

* use pathlib for tar filename

* add cd to gh workspace

* revert workflow changes for python setup/execution

* revert notify event back to on instead of pr

* added arg to post_github_comment to handle contribs

rm notify-docker-available flow

* added bottle2

* debug: add is_contrib flag to docker_login flow

* rm --is_contrib flag from prod flow

* rm dollarsign leftover from circleci docker image url

* debug: add is_contrib flag to docker_login flow

* added circleci node index to image url

* added debug print tree

* debug: force docker_login to fail, trigger contrib flow

* debug: fix circleci artifact filename

* debug: fix circleci artifact filename

* fix docker image size not working in contrib

* debug: print full path to tar

* debug: print full path to tar, attempt 2

* debug: print full path to tar, attempt 3

* debug: print full path to tar, attempt 4

* debug: fix full path to tar

* rm debug prints

* rm bottle2

* rm bottle2 dependabot

* fix tab