The get_version() function in build_source script should be extended to know the latest upstream from git tag

[alee-ntap]

What would you like to be added:

I would like to extend the get_version() function in the build_source script to fetch the latest upstream version from git tags when using git as the upstream source.

Why is this needed:

After investigated on #29 ,
it has been identified that the --create --package $name command results in a version string of gardenlinux~$commit-hash, for example:

+ dch --create --package aws-sdk-cpp --newversion gardenlinux~45805daa1be4515729a226b037e00a726076bb90 --distribution gardenlinux --force-distribution -- 'Rebuild for Garden Linux.' 

To improve the versioning process, it is necessary to modify the get_version() function to fetch the latest upstream version from git tags. This will ensure more accurate and meaningful versioning for the packages.

[nanory]

This task has been completed by #37
I'm closing this issue.