Simpler versioning if release flag is set (#7758)

Simpler versioning if release flag is set (#7758)

Following some discussion, this PR introduces a simpler versioning scheme if the CVC5_IS_RELEASE flag is set.
In our regular versioning scheme, the first commit after release x.y.z has the version x.y.(z+1)-dev.1.abcdef0. Some users however may want to apply some patches, and still have cvc5 show the release version.
With this PR, the version printed (if any commits are present since the tag) is x.y.z-modified if the CVC5_IS_RELEASE flag is still true. We always set it to false immediately after the tagged commit, so it does not change the versions printed by mainline cvc5.