FEATURE: enable support for conditional inclusing of each tag

[LongLiveCHIEF]

Opening this in HackerHappyHour/tagging-strategy#42 as well

---

allow the use of ::true or ::false after each tag to specify whether or not that tag should be produced.

This will allow the use of expressions to determine whether or not a tag should be produced.

Here's a real example: you may want to produce the {{ major }} pattern under most conditions, but it doesn't
make sense to do so in the given tag is a pre-release. You could do something like:

-
  with:
    tags: |
      {{major}}::${{ github.event.action != 'prerelease' }}
      {{major}}.{{minor}}.{{patch}}

[LongLiveCHIEF]

closed in favor of #30

[LongLiveCHIEF]

I'm closing this since I implemented it with the latest release of HackerHappyHour/tagging-strategy, and it's getting to the point with this action IMO where it's too tightly coupled to the workflow event, with too much indirect control and output to really be capable of the flexibility I need. Will open a separate issue with a proposal to redesign ghaction-docker-meta tagging abilities.