Docker Images: Support parsing of tags with one or more colons in tag…

[ninjarobot]

… name.

This PR closes #1068

The changes in this PR are as follows:

• Docker Images: Support parsing of tags with one or more colons in tag name.

I have read the contributing guidelines and have completed the following:

• [ ] Tested my code end-to-end against a live Azure subscription.
• [ ] Updated the documentation in the docs folder for the affected changes.
• [x] Written unit tests against the modified code that I have made.
• [x] Updated the release notes with a new entry for this PR.
• [x] Checked the coding standards outlined in the contributions guide and ensured my code adheres to them.

If I haven't completed any of the tasks above, I include the reasons why here:

Bug was in parsing logic, not in deployment, so nothing to test end to end.