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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`

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

"""Serialize the object into a dictionary."""
        pass
    @abc.abstractmethod
    def generate(self):
        """Generate the resource."""
        pass
    def remove(self, module):
        """Remove the resource from the filesystem."""
        try:
            os.remove(self.path)
            self.changed = True
        except OSError as exc:
            if exc.errno != errno.ENOENT:
                raise OpenSSLObjectError(exc)
            else:
                pass
#
_OID_MAP = {
    '0': ('itu-t', 'ITU-T', 'ccitt'),
    '0.3.4401.5': ('ntt-ds', ),
    '0.3.4401.5.3.1.9': ('camellia', ),
    '0.3.4401.5.3.1.9.1': ('camellia-128-ecb', 'CAMELLIA-128-ECB'),
    '0.3.4401.5.3.1.9.3': ('camellia-128-ofb', 'CAMELLIA-128-OFB'),
    '0.3.4401.5.3.1.9.4': ('camellia-128-cfb', 'CAMELLIA-128-CFB'),
    '0.3.4401.5.3.1.9.6': ('camellia-128-gcm', 'CAMELLIA-128-GCM'),