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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 -->

'1.3.6.1.5.5.7.5.1.3': ('id-regCtrl-pkiPublicationInfo', ),
    '1.3.6.1.5.5.7.5.1.4': ('id-regCtrl-pkiArchiveOptions', ),
    '1.3.6.1.5.5.7.5.1.5': ('id-regCtrl-oldCertID', ),
    '1.3.6.1.5.5.7.5.1.6': ('id-regCtrl-protocolEncrKey', ),
    '1.3.6.1.5.5.7.5.2': ('id-regInfo', ),
    '1.3.6.1.5.5.7.5.2.1': ('id-regInfo-utf8Pairs', ),
    '1.3.6.1.5.5.7.5.2.2': ('id-regInfo-certReq', ),
    '1.3.6.1.5.5.7.6': ('id-alg', ),
    '1.3.6.1.5.5.7.6.1': ('id-alg-des40', ),
    '1.3.6.1.5.5.7.6.2': ('id-alg-noSignature', ),
    '1.3.6.1.5.5.7.6.3': ('id-alg-dh-sig-hmac-sha1', ),
    '1.3.6.1.5.5.7.6.4': ('id-alg-dh-pop', ),
    '1.3.6.1.5.5.7.7': ('id-cmc', ),
    '1.3.6.1.5.5.7.7.1': ('id-cmc-statusInfo', ),
    '1.3.6.1.5.5.7.7.2': ('id-cmc-identification', ),
    '1.3.6.1.5.5.7.7.3': ('id-cmc-identityProof', ),
    '1.3.6.1.5.5.7.7.4': ('id-cmc-dataReturn', ),
    '1.3.6.1.5.5.7.7.5': ('id-cmc-transactionId', ),
    '1.3.6.1.5.5.7.7.6': ('id-cmc-senderNonce', ),
    '1.3.6.1.5.5.7.7.7': ('id-cmc-recipientNonce', ),
    '1.3.6.1.5.5.7.7.8': ('id-cmc-addExtensions', ),
    '1.3.6.1.5.5.7.7.9': ('id-cmc-encryptedPOP', ),
    '1.3.6.1.5.5.7.7.10': ('id-cmc-decryptedPOP', ),
    '1.3.6.1.5.5.7.7.11': ('id-cmc-lraPOPWitness', ),
    '1.3.6.1.5.5.7.7.15': ('id-cmc-getCert', ),
    '1.3.6.1.5.5.7.7.16': ('id-cmc-getCRL', ),
    '1.3.6.1.5.5.7.7.17': ('id-cmc-revokeRequest', ),
    '1.3.6.1.5.5.7.7.18': ('id-cmc-regInfo', ),
    '1.3.6.1.5.5.7.7.19': ('id-cmc-responseInfo', ),
    '1.3.6.1.5.5.7.7.21': ('id-cmc-queryPending', ),