Add tag filtering for offline_packages and republish_images

[andrew-su]

Summary

This change addresses #537. It adds a new parameter of tag_prefix which by default is empty. If it is specified, only tags with that specific prefix is listed.

If the tag was my-buildpack/v1.2.3 then the expected tag_prefix should be my-buildpack/.

Use Cases

Some repos may use a prefix on their tags. For example: my-buildpack/v1.2.3, my-buildpack/2.3.4 or my-buildpack-v1.2.3

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).

[dmikusa]

@andrew-su - Sorry. Not sure if I should have merged these in the opposite order, but there are some merge conflicts now. Do you have a chance to take a look and resolve them? Thanks

[andrew-su]

I didn't base the work here off the other branch, I've rebased it now.

[dmikusa]

Thanks!