Bump container registry to v3.20.0

What does this MR do?

3.20.0 (2021-12-30)

Bug Fixes

• datastore: check for blob access before importing layer (84cf639)
• datastore: skip caching of large configuration payloads (748dbaa)
• remove temporary log entries for "finding repository by path" queries (090e34c)

Features

• add Google CDN support (612e861)
• handlers/configuration: enable manifest payload size limit (db18ba1)

Related issues

Related to gitlab-org/container-registry#549 (closed) and https://gitlab.com/gitlab-org/container-registry/-/issues/535.

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Integration tests added to GitLab QA
• The impact any change in container size has should be evaluated