Add state option to git_config module (#50578)

* Add state option to git_config module

State present/absent option works like --set/--unset option for 'git config'.

* Change git_config to avoid useless parameter passed to git command

When unsetting value, command was : git config --unset foo ''.
Now command is : git config --unset foo.

* Add some integration tests to git_config module

* Add missing aliases file

* Change set up method

Using git command seems to cause troubles on some OS : changing config
by changing '.gitconfig' file.

* Remove some distros from tests pool

Git is not installed or is out of date on these distros.

* Fix aliases to skip tests on centos6

* Refactor tests of the git_config module

* Add use case when state=absent and value is defined

test/integration/targets/git_config/tasks/setup.yml

@@ -0,0 +1,11 @@
+---
+- name: verify that git is installed so this test can continue
+  command: which git
+  register: git_installed
+  ignore_errors: yes
+
+- name: get git version, only newer than {{git_version_supporting_includes}} has includes option
+  shell: "git --version | grep 'git version' | sed 's/git version //'"
+  register: git_version
+  ignore_errors: yes
+...