Refactor generic git functions into git module

[r-richardson]

Refactor generic git related functions from OpenQA::Task::Git::Clone into the OpenQA::Git module for easier re-usability.
Related Ticket: 164886

[okurz]

If this is a prerequisite step for using the functions in other places then this looks good. If it stays like this then I am against at as functions that are only used once should be as close as possible where needed. We already discussed the possibility to keep the state within the object so that not every command needs to re-initialize or something

[perlpunk]

We discussed a few things.
OpenQA::Git so far returns undef for success and the error message for a failure.
The new functions use die, and I like that more, as failures cannot be accidentally ignored, but must be catched with an eval.
We should decide on one or the other.

As another improvement I suggest another helper. Instead of

sub get_current_branch ($self) {
    my @git = $self->_prepare_git_command();
    my $r = run_cmd_with_log_return_error([@git, 'branch', '--show-current']);

we could do

sub _run_cmd ($self, $args) {
    my @git = $self->_prepare_git_command();
    return run_cmd_with_log_return_error([@git, @$args]);
}
...
sub get_current_branch ($self) {
    my $r = $self->_run_cmd(['branch', '--show-current']);

[perlpunk]

If it stays like this then I am against at as functions that are only used once should be as close as possible where needed.

But the point of the ticket is to move all git functions to OpenQA::Git. if you are against this, we should have discussed this in the estimation.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.51%. Comparing base (ceffdd8) to head (e7eb938).
Report is 20 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5863   +/-   ##
=======================================
  Coverage   98.51%   98.51%           
=======================================
  Files         395      395           
  Lines       38782    38797   +15     
=======================================
+ Hits        38205    38220   +15     
  Misses        577      577           

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[perlpunk]

Somehow git thinks I have started and never finished a review, so it's pending.
So I just try to submit it although I don't know what is still pending.

Reviewer will be absent for a while