Add a flag `--upstream-version` to migrate a package to an other vers…

[lecler-i]

…ion.

This is useful if you wanna import a centos7 package into rocky9.

Example, I want to have ansible-2.9.27 that is available on EPEL7 on my rocky9 repos.

srpmproc \
  --import-branch-prefix "epel"\
  --rpm-prefix "https://src.fedoraproject.org/rpms/"\
  --version 7\
  --upstream-prefix file:///tmp/upstream/git/ \
  --upstream-version 9\
  --branch-prefix "r"\
  --cdn fedora\
  --source-rpm ansible\
  --storage-addr 'file:///tmp/s3/'

You can obviously use it backward, to port a fancy package from rocky9 to your old centos7 infra.

I didn't do anything related to patches tho.