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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 -->

'1.3.132.0.31': ('secp192k1', ),
    '1.3.132.0.32': ('secp224k1', ),
    '1.3.132.0.33': ('secp224r1', ),
    '1.3.132.0.34': ('secp384r1', ),
    '1.3.132.0.35': ('secp521r1', ),
    '1.3.132.0.36': ('sect409k1', ),
    '1.3.132.0.37': ('sect409r1', ),
    '1.3.132.0.38': ('sect571k1', ),
    '1.3.132.0.39': ('sect571r1', ),
    '1.3.132.1': ('secg-scheme', ),
    '1.3.132.1.11.0': ('dhSinglePass-stdDH-sha224kdf-scheme', ),
    '1.3.132.1.11.1': ('dhSinglePass-stdDH-sha256kdf-scheme', ),
    '1.3.132.1.11.2': ('dhSinglePass-stdDH-sha384kdf-scheme', ),
    '1.3.132.1.11.3': ('dhSinglePass-stdDH-sha512kdf-scheme', ),
    '1.3.132.1.14.0': ('dhSinglePass-cofactorDH-sha224kdf-scheme', ),
    '1.3.132.1.14.1': ('dhSinglePass-cofactorDH-sha256kdf-scheme', ),
    '1.3.132.1.14.2': ('dhSinglePass-cofactorDH-sha384kdf-scheme', ),
    '1.3.132.1.14.3': ('dhSinglePass-cofactorDH-sha512kdf-scheme', ),
    '1.3.133.16.840.63.0': ('x9-63-scheme', ),
    '1.3.133.16.840.63.0.2': ('dhSinglePass-stdDH-sha1kdf-scheme', ),
    '1.3.133.16.840.63.0.3': ('dhSinglePass-cofactorDH-sha1kdf-scheme', ),
    '2': ('joint-iso-itu-t', 'JOINT-ISO-ITU-T', 'joint-iso-ccitt'),
    '2.5': ('directory services (X.500)', 'X500'),
    '2.5.1.5': ('Selected Attribute Types', 'selected-attribute-types'),
    '2.5.1.5.55': ('clearance', ),
    '2.5.4': ('X509', ),
    '2.5.4.3': ('commonName', 'CN'),
    '2.5.4.4': ('surname', 'SN'),
    '2.5.4.5': ('serialNumber', ),
    '2.5.4.6': ('countryName', 'C'),