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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 -->

'0.9.2342.19200300.100.1.9': ('host', ),
    '0.9.2342.19200300.100.1.10': ('manager', ),
    '0.9.2342.19200300.100.1.11': ('documentIdentifier', ),
    '0.9.2342.19200300.100.1.12': ('documentTitle', ),
    '0.9.2342.19200300.100.1.13': ('documentVersion', ),
    '0.9.2342.19200300.100.1.14': ('documentAuthor', ),
    '0.9.2342.19200300.100.1.15': ('documentLocation', ),
    '0.9.2342.19200300.100.1.20': ('homeTelephoneNumber', ),
    '0.9.2342.19200300.100.1.21': ('secretary', ),
    '0.9.2342.19200300.100.1.22': ('otherMailbox', ),
    '0.9.2342.19200300.100.1.23': ('lastModifiedTime', ),
    '0.9.2342.19200300.100.1.24': ('lastModifiedBy', ),
    '0.9.2342.19200300.100.1.25': ('domainComponent', 'DC'),
    '0.9.2342.19200300.100.1.26': ('aRecord', ),
    '0.9.2342.19200300.100.1.27': ('pilotAttributeType27', ),
    '0.9.2342.19200300.100.1.28': ('mXRecord', ),
    '0.9.2342.19200300.100.1.29': ('nSRecord', ),
    '0.9.2342.19200300.100.1.30': ('sOARecord', ),
    '0.9.2342.19200300.100.1.31': ('cNAMERecord', ),
    '0.9.2342.19200300.100.1.37': ('associatedDomain', ),
    '0.9.2342.19200300.100.1.38': ('associatedName', ),
    '0.9.2342.19200300.100.1.39': ('homePostalAddress', ),
    '0.9.2342.19200300.100.1.40': ('personalTitle', ),
    '0.9.2342.19200300.100.1.41': ('mobileTelephoneNumber', ),
    '0.9.2342.19200300.100.1.42': ('pagerTelephoneNumber', ),
    '0.9.2342.19200300.100.1.43': ('friendlyCountryName', ),
    '0.9.2342.19200300.100.1.44': ('uniqueIdentifier', 'uid'),
    '0.9.2342.19200300.100.1.45': ('organizationalStatus', ),
    '0.9.2342.19200300.100.1.46': ('janetMailbox', ),
    '0.9.2342.19200300.100.1.47': ('mailPreferenceOption', ),