Use GH Actions for triggering Tugboat previews

[BWpanda]

In an effort to avoid hitting our Tugboat quota, I'd like to make it so that you can 'skip' building a Tugboat preview site for certain PRs (e.g. documentation-only changes, updates to CI tests, etc.). In cases like these it doesn't make sense to have a Tugboat preview, so you would add specific text to the PR title or commit message (e.g. [skip tugboat]), then Tugboat wouldn't run (this saves building unnecessary previews and hitting our quota more frequently). Unfortunately though, this is not currently possible with Tugboat.

I reached out to them and suggested this as a possible new feature, and while they said they'll investigate the possibility, they also suggested using GitHub Actions instead to trigger the Tugboat build. This would provide more customisability, including checking for a certain tag in the PR title/commit message and skipping the build if present. (Since Tugboat support GitHub, GitLab and BitBucket, they don't provide specific solutions for each system (i.e. there's no Tugboat action for GH already))

So I will try looking into the possibility of setting up a GH action for Tugboat, and deprecating the current Tugboat functionality. Not sure if it'll work or be worthwhile though...