Add action for automatically version bumping merges to master.

[nerrad]

It'd be really handy for testing purposes to know exactly what development version is being tested. So the idea here is that:

• when a merge to master occurs
• if the version in package.json contains a -dev suffix, then version bump the micro version (eg. 3.2.0.001-dev)
• if the version in package.json does not contain a -dev suffix, then bump the minor version and add dev. (eg. 3.2.0 would become 3.3.0.001-dev.
• commit version bump and push (using a separate Github action). Potentially, we could append the commit to the merge commit (and force push) so that it keeps git history clean. There's some risk with that though as it means checked out branches could have incorrect history. Would have to test that approach first.

[nerrad]

Alternatively, the micro version bump could create more noise than we want in the repo, so we could just start with the non-dev version detection bumped to dev version.