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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 -->

'0.9.2342.19200300.100.1.48': ('buildingName', ),
    '0.9.2342.19200300.100.1.49': ('dSAQuality', ),
    '0.9.2342.19200300.100.1.50': ('singleLevelQuality', ),
    '0.9.2342.19200300.100.1.51': ('subtreeMinimumQuality', ),
    '0.9.2342.19200300.100.1.52': ('subtreeMaximumQuality', ),
    '0.9.2342.19200300.100.1.53': ('personalSignature', ),
    '0.9.2342.19200300.100.1.54': ('dITRedirect', ),
    '0.9.2342.19200300.100.1.55': ('audio', ),
    '0.9.2342.19200300.100.1.56': ('documentPublisher', ),
    '0.9.2342.19200300.100.3': ('pilotAttributeSyntax', ),
    '0.9.2342.19200300.100.3.4': ('iA5StringSyntax', ),
    '0.9.2342.19200300.100.3.5': ('caseIgnoreIA5StringSyntax', ),
    '0.9.2342.19200300.100.4': ('pilotObjectClass', ),
    '0.9.2342.19200300.100.4.3': ('pilotObject', ),
    '0.9.2342.19200300.100.4.4': ('pilotPerson', ),
    '0.9.2342.19200300.100.4.5': ('account', ),
    '0.9.2342.19200300.100.4.6': ('document', ),
    '0.9.2342.19200300.100.4.7': ('room', ),
    '0.9.2342.19200300.100.4.9': ('documentSeries', ),
    '0.9.2342.19200300.100.4.13': ('Domain', 'domain'),
    '0.9.2342.19200300.100.4.14': ('rFC822localPart', ),
    '0.9.2342.19200300.100.4.15': ('dNSDomain', ),
    '0.9.2342.19200300.100.4.17': ('domainRelatedObject', ),
    '0.9.2342.19200300.100.4.18': ('friendlyCountry', ),
    '0.9.2342.19200300.100.4.19': ('simpleSecurityObject', ),
    '0.9.2342.19200300.100.4.20': ('pilotOrganization', ),
    '0.9.2342.19200300.100.4.21': ('pilotDSA', ),
    '0.9.2342.19200300.100.4.22': ('qualityLabelledData', ),
    '0.9.2342.19200300.100.10': ('pilotGroups', ),
    '1': ('iso', 'ISO'),