Overview
Currently, libgit2 provides commit signing with GPG but does not provide tag signing. The ability to sign tags with libgit2 is important because it is difficult to apply security practices without automation.

Please implement this so that I may extend pygit2 also.

Thank you

References
#3673
https://libgit2.org/libgit2/#HEAD/group/commit/git_commit_create_buffer
https://libgit2.org/libgit2/#HEAD/group/commit/git_commit_create_with_signature
libgit2/pygit2#1142