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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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export_format = cryptography.hazmat.primitives.serialization.PrivateFormat.TraditionalOpenSSL
        try:
            if self.type == 'RSA':
                self.privatekey = cryptography.hazmat.primitives.asymmetric.rsa.generate_private_key(
                    public_exponent=65537,  
                    key_size=self.size,
                    backend=self.cryptography_backend
                )
            if self.type == 'DSA':
                self.privatekey = cryptography.hazmat.primitives.asymmetric.dsa.generate_private_key(
                    key_size=self.size,
                    backend=self.cryptography_backend
                )
            if CRYPTOGRAPHY_HAS_X25519_FULL and self.type == 'X25519':
                self.privatekey = cryptography.hazmat.primitives.asymmetric.x25519.X25519PrivateKey.generate()
                export_format = cryptography.hazmat.primitives.serialization.PrivateFormat.PKCS8
            if CRYPTOGRAPHY_HAS_X448 and self.type == 'X448':
                self.privatekey = cryptography.hazmat.primitives.asymmetric.x448.X448PrivateKey.generate()
                export_format = cryptography.hazmat.primitives.serialization.PrivateFormat.PKCS8
            if CRYPTOGRAPHY_HAS_ED25519 and self.type == 'Ed25519':
                self.privatekey = cryptography.hazmat.primitives.asymmetric.ed25519.Ed25519PrivateKey.generate()
                export_format = cryptography.hazmat.primitives.serialization.PrivateFormat.PKCS8
            if CRYPTOGRAPHY_HAS_ED448 and self.type == 'Ed448':
                self.privatekey = cryptography.hazmat.primitives.asymmetric.ed448.Ed448PrivateKey.generate()
                export_format = cryptography.hazmat.primitives.serialization.PrivateFormat.PKCS8
            if self.type == 'ECC' and self.curve in self.curves:
                if self.curves[self.curve]['deprecated']:
                    self.module.warn('Elliptic curves of type {0} should not be used for new keys!'.format(self.curve))