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##### SUMMARY

The Git module encourages use of `StrictHostKeyChecking=no` with SSH, which makes the connection vulnerable to a MITM attack.

##### ISSUE TYPE

OpenSSH 7.5+ (2017-03-20) added a safer option which automatically accepts the key on first use but will not allow a MITM on subsequent connections: `StrictHostKeyChecking=accept-new` 

https://man.openbsd.org/ssh_config#StrictHostKeyChecking

It would be great if Ansible encouraged use of that mode by default in the documentation and to implement features such as the Git module's [`accept_hostkey`](https://github.com/ansible/ansible/blob/323d2adfcce9a53e906c2c4a40f6ac5fb32a0e68/lib/ansible/modules/git.py#L1103-L1108) feature.

##### ANSIBLE VERSION

```paste below
N/A
```

##### COMPONENT NAME
* `/modules/source_control/git.py`


changed = False
    if not os.path.exists(os.path.join(dest, '.gitmodules')):
        
        return changed
    gitmodules_file = open(os.path.join(dest, '.gitmodules'), 'r')
    for line in gitmodules_file:
        
        if not changed and line.strip().startswith('path'):
            path = line.split('=', 1)[1].strip()
            
            if not os.path.exists(os.path.join(dest, path, '.git')):
                changed = True
    
    if not changed:
        
        begin = get_submodule_versions(git_path, module, dest)
        cmd = [git_path, 'submodule', 'foreach', git_path, 'fetch']
        (rc, out, err) = module.run_command(cmd, check_rc=True, cwd=dest)
        if rc != 0:
            module.fail_json(msg="Failed to fetch submodules: %s" % out + err)
        if track_submodules:
            
            
            version = 'master'
            after = get_submodule_versions(git_path, module, dest, '%s/%s' % (remote, version))
            if begin != after:
                changed = True
        else: