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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 -->

'1.3.6.1.5.5.7.1.1': ('Authority Information Access', 'authorityInfoAccess'),
    '1.3.6.1.5.5.7.1.2': ('Biometric Info', 'biometricInfo'),
    '1.3.6.1.5.5.7.1.3': ('qcStatements', ),
    '1.3.6.1.5.5.7.1.4': ('ac-auditEntity', ),
    '1.3.6.1.5.5.7.1.5': ('ac-targeting', ),
    '1.3.6.1.5.5.7.1.6': ('aaControls', ),
    '1.3.6.1.5.5.7.1.7': ('sbgp-ipAddrBlock', ),
    '1.3.6.1.5.5.7.1.8': ('sbgp-autonomousSysNum', ),
    '1.3.6.1.5.5.7.1.9': ('sbgp-routerIdentifier', ),
    '1.3.6.1.5.5.7.1.10': ('ac-proxying', ),
    '1.3.6.1.5.5.7.1.11': ('Subject Information Access', 'subjectInfoAccess'),
    '1.3.6.1.5.5.7.1.14': ('Proxy Certificate Information', 'proxyCertInfo'),
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