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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 -->

'1.2.840.10045.3.1.1': ('prime192v1', ),
    '1.2.840.10045.3.1.2': ('prime192v2', ),
    '1.2.840.10045.3.1.3': ('prime192v3', ),
    '1.2.840.10045.3.1.4': ('prime239v1', ),
    '1.2.840.10045.3.1.5': ('prime239v2', ),
    '1.2.840.10045.3.1.6': ('prime239v3', ),
    '1.2.840.10045.3.1.7': ('prime256v1', ),
    '1.2.840.10045.4': ('id-ecSigType', ),
    '1.2.840.10045.4.1': ('ecdsa-with-SHA1', ),
    '1.2.840.10045.4.2': ('ecdsa-with-Recommended', ),
    '1.2.840.10045.4.3': ('ecdsa-with-Specified', ),
    '1.2.840.10045.4.3.1': ('ecdsa-with-SHA224', ),
    '1.2.840.10045.4.3.2': ('ecdsa-with-SHA256', ),
    '1.2.840.10045.4.3.3': ('ecdsa-with-SHA384', ),
    '1.2.840.10045.4.3.4': ('ecdsa-with-SHA512', ),
    '1.2.840.10046.2.1': ('X9.42 DH', 'dhpublicnumber'),
    '1.2.840.113533.7.66.10': ('cast5-cbc', 'CAST5-CBC'),
    '1.2.840.113533.7.66.12': ('pbeWithMD5AndCast5CBC', ),
    '1.2.840.113533.7.66.13': ('password based MAC', 'id-PasswordBasedMAC'),
    '1.2.840.113533.7.66.30': ('Diffie-Hellman based MAC', 'id-DHBasedMac'),
    '1.2.840.113549': ('RSA Data Security, Inc.', 'rsadsi'),
    '1.2.840.113549.1': ('RSA Data Security, Inc. PKCS', 'pkcs'),
    '1.2.840.113549.1.1': ('pkcs1', ),
    '1.2.840.113549.1.1.1': ('rsaEncryption', ),
    '1.2.840.113549.1.1.2': ('md2WithRSAEncryption', 'RSA-MD2'),
    '1.2.840.113549.1.1.3': ('md4WithRSAEncryption', 'RSA-MD4'),
    '1.2.840.113549.1.1.4': ('md5WithRSAEncryption', 'RSA-MD5'),
    '1.2.840.113549.1.1.5': ('sha1WithRSAEncryption', 'RSA-SHA1'),
    '1.2.840.113549.1.1.6': ('rsaOAEPEncryptionSET', ),
    '1.2.840.113549.1.1.7': ('rsaesOaep', 'RSAES-OAEP'),