Add version flag to generator

[dhaiducek]

Adds a generator version flag with the Git SHA in the output:

v1.12.2-ab49eaf2a21d44265784bbd1f8381ec6e8928828

Also adds verification that the VERSION.txt file was updated so that a release isn't created without the version being updated.

This is my first time adding version information to anything, so if anyone has other ideas/pointers, do share!

ref: https://issues.redhat.com/browse/ACM-5803

Closes #118

[dhaiducek]

I've used @JustinKuli's idea in the latest code to default with fallbacks in the following order:

1. Native git describe output when available (v1.12.1-3-gaa03f1c)
2. <branch>-<Git SHA> when tags aren't available like in Stolostron (release-2.9-8466f8c)
3. <git SHA>-dev when a branch isn't available like a detached HEAD (8466f8c-dev)
4. Default string Unversioned binary when built without setting Version variable

We could maybe add the org in there, but this ought to be enough information/fallbacks to find the version at play (or figure out that it wasn't built by us).

[JustinKuli]

/hold for @mprahl

This seems nicely automatic for now, with the possibility to override the setting for specific use cases in the future if we ever need to.

[mprahl]

Why do we want to use --dirty?

[dhaiducek]

More of a safety/notification thing than anything. Without it, the -dirty suffix isn't added when there have been local changes:

When the working tree matches HEAD, the output is the same as "git describe HEAD". If the working tree has local modification "-dirty" is appended to it.

https://git-scm.com/docs/git-describe#Documentation/git-describe.txt---dirtyltmarkgt

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dhaiducek, JustinKuli, mprahl, yiraeChristineKim

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[dhaiducek]

/unhold