<!--- Verify first that your feature was not already discussed on GitHub -->
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##### SUMMARY
<!--- Describe the new feature/improvement briefly below -->
The `ssh_opts` parameter relies on setting environment variables for git, such as GIT_SSH. Git did not recognize this environment variable until version 2.3.0 (see https://git-scm.com/docs/git/2.3.0), and many contemporary OSes (RHEL 7, CentOS7) include older versions of Git (1.8.3.1).

It would be useful to provide a warning in this case, similar to the warning for the `depth` parameter. E.g. "Your git version is too old to support the ssh_opts argument."

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
git.py
source control, git module

##### ADDITIONAL INFORMATION
<!--- Describe how the feature would be used, why it is needed and what it would solve -->
It would save users time when trying to troubleshoot failed git connections via SSH.

<!--- Paste example playbooks or commands between quotes below -->
```yaml
- name: clone a git repo
  git:
    repo: git@github.com:cherdt/hello_ansible.git
    dest: /opt/hello_ansible
    version: master
    ssh_opts: "{{-o IdentityFile=github_id_rsa}}"
```

<!--- HINT: You can also paste gist.github.com links for larger files -->

type: path
        required: true
    version:
        description:
            - What version of the repository to check out. This can be
              the literal string C(HEAD), a branch name, a tag name.
              It can also be a I(SHA-1) hash, in which case I(refspec) needs
              to be specified if the given revision is not already available.
        type: str
        default: "HEAD"
    accept_hostkey:
        description:
            - If C(yes), ensure that "-o StrictHostKeyChecking=no" is
              present as an ssh option.
        type: bool
        default: 'no'
        version_added: "1.5"
    accept_newhostkey:
        description:
            - As of OpenSSH 7.5, "-o StrictHostKeyChecking=accept-new" can be
              used which is safer and will only accepts host keys which are
              not present or are the same. if C(yes), ensure that
              "-o StrictHostKeyChecking=accept-new" is present as an ssh option.
        type: bool
        default: 'no'
        version_added: "2.12"
    ssh_opts:
        description:
            - Creates a wrapper script and exports the path as GIT_SSH
              which git then automatically uses to override ssh arguments.