Enforce release tags on merges into master (i.e. release bumps)

[lukpueh]

#87 added versioning/release policies, plus a script that helps to enforce them. One of the policies is:

Merges with 'master' must be followed by a git tag for the new version number.

This policy is not enforced by the script, as the script is auto-executed on PRs, but this policy would need to be enforced post-merge.

It would be nice to either:

• auto-tag on merge into master ( see Add specification versioning- and release management instructions and checks #87 (comment)), or
• otherwise insistently remind the maintainer to tag the release

[joshuagl]

I really like the idea of auto-tag on merge to master, we could use something like this GitHub Action to enable that workflow https://github.com/marketplace/actions/automatic-releases

[trishankatdatadog]

The Agent integrations workflows might be helpful to read, too...

Cc @ofek

[lukpueh]

otherwise insistently remind the maintainer to tag the release

We could have the release policy checker script on Travis post these lines as a comment using the GitHub API.

Might be a fun self-contained task for a student (cc @SantiagoTorres, @adityasaky)

[joshuagl]

We did this in #148