<!--- Verify first that your feature was not already discussed on GitHub -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### 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 -->

archive_prefix:
        description:
            - Specify a prefix to add to each file path in archive. Requires I(archive) to be specified.
        version_added: "2.10"
        type: str
    separate_git_dir:
        description:
            - The path to place the cloned repository. If specified, Git repository
              can be separated from working tree.
        type: path
        version_added: "2.7"
    gpg_whitelist:
        description:
           - A list of trusted GPG fingerprints to compare to the fingerprint of the
             GPG-signed commit.
           - Only used when I(verify_commit=yes).
           - Use of this feature requires Git 2.6+ due to its reliance on git's C(--raw) flag to C(verify-commit) and C(verify-tag).
        type: list
        elements: str
        default: []
        version_added: "2.9"
requirements:
    - git>=1.7.1 (the command line tool)
attributes:
    check_mode:
        support: full
    diff_mode:
        support: full
    platform:
        platforms: posix