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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 -->

'1.2.840.113549.1.9.22.1': ('x509Certificate', ),
    '1.2.840.113549.1.9.22.2': ('sdsiCertificate', ),
    '1.2.840.113549.1.9.23': ('crlTypes', ),
    '1.2.840.113549.1.9.23.1': ('x509Crl', ),
    '1.2.840.113549.1.12': ('pkcs12', ),
    '1.2.840.113549.1.12.1': ('pkcs12-pbeids', ),
    '1.2.840.113549.1.12.1.1': ('pbeWithSHA1And128BitRC4', 'PBE-SHA1-RC4-128'),
    '1.2.840.113549.1.12.1.2': ('pbeWithSHA1And40BitRC4', 'PBE-SHA1-RC4-40'),
    '1.2.840.113549.1.12.1.3': ('pbeWithSHA1And3-KeyTripleDES-CBC', 'PBE-SHA1-3DES'),
    '1.2.840.113549.1.12.1.4': ('pbeWithSHA1And2-KeyTripleDES-CBC', 'PBE-SHA1-2DES'),
    '1.2.840.113549.1.12.1.5': ('pbeWithSHA1And128BitRC2-CBC', 'PBE-SHA1-RC2-128'),
    '1.2.840.113549.1.12.1.6': ('pbeWithSHA1And40BitRC2-CBC', 'PBE-SHA1-RC2-40'),
    '1.2.840.113549.1.12.10': ('pkcs12-Version1', ),
    '1.2.840.113549.1.12.10.1': ('pkcs12-BagIds', ),
    '1.2.840.113549.1.12.10.1.1': ('keyBag', ),
    '1.2.840.113549.1.12.10.1.2': ('pkcs8ShroudedKeyBag', ),
    '1.2.840.113549.1.12.10.1.3': ('certBag', ),
    '1.2.840.113549.1.12.10.1.4': ('crlBag', ),
    '1.2.840.113549.1.12.10.1.5': ('secretBag', ),
    '1.2.840.113549.1.12.10.1.6': ('safeContentsBag', ),
    '1.2.840.113549.2.2': ('md2', 'MD2'),
    '1.2.840.113549.2.4': ('md4', 'MD4'),
    '1.2.840.113549.2.5': ('md5', 'MD5'),
    '1.2.840.113549.2.6': ('hmacWithMD5', ),
    '1.2.840.113549.2.7': ('hmacWithSHA1', ),
    '1.2.840.113549.2.8': ('hmacWithSHA224', ),
    '1.2.840.113549.2.9': ('hmacWithSHA256', ),
    '1.2.840.113549.2.10': ('hmacWithSHA384', ),
    '1.2.840.113549.2.11': ('hmacWithSHA512', ),
    '1.2.840.113549.2.12': ('hmacWithSHA512-224', ),