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##### SUMMARY
Allow to specify a new "format" parameter in "openssl_privatekey". Today the output format is decided by a very simple heuristic which requires further commands to work properly.
I need, for example, to generate a RSA private key but in PKCS8 format. The current heuristic uses OpenSSH format for RSA keys and only uses PKCS8 for Ed25519 and similar. This makes me use a "command" with "openssl" to convert the generated key, which leads to idempotency problems and unnecessary complexity.

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME
openssl_privatekey

##### ADDITIONAL INFORMATION
<!--- Describe how the feature would be used, why it is needed and what it would solve -->
The current heuristic should be kept unless overwritten by user.

<!--- Paste example playbooks or commands between quotes below -->
```yaml
openssl_privatekey:
  path: /etc/ssl/private/ansible.com.pem
  format: pkcs8
```
The values allowed are `pkcs1`, `raw` and `pkcs8`

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digest = None
    if digest_string == 'sha256':
        digest = hashes.SHA256()
    elif digest_string == 'sha384':
        digest = hashes.SHA384()
    elif digest_string == 'sha512':
        digest = hashes.SHA512()
    elif digest_string == 'sha1':
        digest = hashes.SHA1()
    elif digest_string == 'md5':
        digest = hashes.MD5()
    return digest
def write_file(module, content, default_mode=None, path=None):
    '''
    Writes content into destination file as securely as possible.
    Uses file arguments from module.
    '''
    
    file_args = module.load_file_common_arguments(module.params)
    if file_args['mode'] is None:
        file_args['mode'] = default_mode
    
    if path is not None:
        file_args['path'] = path
    
    tmp_fd, tmp_name = tempfile.mkstemp(prefix=b'.ansible_tmp')
    try:
        os.close(tmp_fd)