feat: set version equal to module version

[codyoss]

As of googleapis/google-cloud-go#5517 we
now have a version file in the internal package for every module.
This change reads variable and uses it for the client version. This
means all autogenerated clients will now get a meaningful realease
version in thier call metadata.

[codyoss]

@noahdietz This is a little hacky but something roughly like this is what I was thinking... LMK WYT

[noahdietz]

I want to make this happen because it will be useful. My main concern is that a Go gapic is no longer compilable without the addition of the internal.Version variable. Let's figure out how we can overcome that. Perhaps with a flag of some sort that we only use in our regen pipeline? Or does the generator also generate that file with var Version = 0.1.0, and our pipeline only copies the generated file on the first generation of the pkg?