Create flow for automating byte-buddy version bump

[hughsimpson]

Automates bumping byte-buddy versions. Since bumps will, presumably, mostly be triggered off personal forks, it's not possible to push the bot commit directly to the branch. Additionally, without providing a personal access token, it's not possible for the github actions bot to directly trigger the test workflow. So, the flow is a little more convoluted than I'd like, but still feels more streamlined and preserves provenance. I've tested the following flow locally against my own fork:

• Open up a pr to master with an updated byte-buddy-tag (eg. test url change hughsimpson/kanela#10)
• The new action will then automatically build byte-buddy with the patch and open a pr corresponding to the bump (c.f update byte buddy tag byte buddy 1.15.0 hughsimpson/kanela#11)
• Tests can then be triggered by the comment please rerun tests -- this gets around the restriction that bot commits can't trigger workflows.

You'll have noticed that the new workflow is failing in this pr.. That's because, by adding the byte-buddy-tag file I've triggered the constraint, but the workflow permissions (specifically pull-requests: write and contents: write) don't take effect until merged. Linked to my fork so you can see that it does, in fact, work once merged :)

cc @ivantopo @dpsoft thoughts on this? I believe it could be made more streamlined with a personal access token set by a repo owner, but since I'm not one, this is pretty much the best I think I can do...

[hughsimpson]

@dpsoft any comments on this?

[dpsoft]

@hughsimpson LGTM.

[hughsimpson]

Thanks @dpsoft . I don't have perms, could you do the honours? I'll try out out once it's merged so you should see a follow-up with the lib bump 🤞

[dpsoft]

@hughsimpson done!