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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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self._add_curve('secp256r1', 'SECP256R1')
        self._add_curve('secp256k1', 'SECP256K1')
        self._add_curve('brainpoolP256r1', 'BrainpoolP256R1', deprecated=True)
        self._add_curve('brainpoolP384r1', 'BrainpoolP384R1', deprecated=True)
        self._add_curve('brainpoolP512r1', 'BrainpoolP512R1', deprecated=True)
        self._add_curve('sect571k1', 'SECT571K1', deprecated=True)
        self._add_curve('sect409k1', 'SECT409K1', deprecated=True)
        self._add_curve('sect283k1', 'SECT283K1', deprecated=True)
        self._add_curve('sect233k1', 'SECT233K1', deprecated=True)
        self._add_curve('sect163k1', 'SECT163K1', deprecated=True)
        self._add_curve('sect571r1', 'SECT571R1', deprecated=True)
        self._add_curve('sect409r1', 'SECT409R1', deprecated=True)
        self._add_curve('sect283r1', 'SECT283R1', deprecated=True)
        self._add_curve('sect233r1', 'SECT233R1', deprecated=True)
        self._add_curve('sect163r2', 'SECT163R2', deprecated=True)
        self.module = module
        self.cryptography_backend = cryptography.hazmat.backends.default_backend()
        self.type = module.params['type']
        self.curve = module.params['curve']
        if not CRYPTOGRAPHY_HAS_X25519 and self.type == 'X25519':
            self.module.fail_json(msg='Your cryptography version does not support X25519')
        if not CRYPTOGRAPHY_HAS_X25519_FULL and self.type == 'X25519':
            self.module.fail_json(msg='Your cryptography version does not support X25519 serialization')
        if not CRYPTOGRAPHY_HAS_X448 and self.type == 'X448':
            self.module.fail_json(msg='Your cryptography version does not support X448')
        if not CRYPTOGRAPHY_HAS_ED25519 and self.type == 'Ed25519':
            self.module.fail_json(msg='Your cryptography version does not support Ed25519')
        if not CRYPTOGRAPHY_HAS_ED448 and self.type == 'Ed448':
            self.module.fail_json(msg='Your cryptography version does not support Ed448')
    def _generate_private_key_data(self):