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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 -->

'0.3.4401.5.3.1.9.7': ('camellia-128-ccm', 'CAMELLIA-128-CCM'),
    '0.3.4401.5.3.1.9.9': ('camellia-128-ctr', 'CAMELLIA-128-CTR'),
    '0.3.4401.5.3.1.9.10': ('camellia-128-cmac', 'CAMELLIA-128-CMAC'),
    '0.3.4401.5.3.1.9.21': ('camellia-192-ecb', 'CAMELLIA-192-ECB'),
    '0.3.4401.5.3.1.9.23': ('camellia-192-ofb', 'CAMELLIA-192-OFB'),
    '0.3.4401.5.3.1.9.24': ('camellia-192-cfb', 'CAMELLIA-192-CFB'),
    '0.3.4401.5.3.1.9.26': ('camellia-192-gcm', 'CAMELLIA-192-GCM'),
    '0.3.4401.5.3.1.9.27': ('camellia-192-ccm', 'CAMELLIA-192-CCM'),
    '0.3.4401.5.3.1.9.29': ('camellia-192-ctr', 'CAMELLIA-192-CTR'),
    '0.3.4401.5.3.1.9.30': ('camellia-192-cmac', 'CAMELLIA-192-CMAC'),
    '0.3.4401.5.3.1.9.41': ('camellia-256-ecb', 'CAMELLIA-256-ECB'),
    '0.3.4401.5.3.1.9.43': ('camellia-256-ofb', 'CAMELLIA-256-OFB'),
    '0.3.4401.5.3.1.9.44': ('camellia-256-cfb', 'CAMELLIA-256-CFB'),
    '0.3.4401.5.3.1.9.46': ('camellia-256-gcm', 'CAMELLIA-256-GCM'),
    '0.3.4401.5.3.1.9.47': ('camellia-256-ccm', 'CAMELLIA-256-CCM'),
    '0.3.4401.5.3.1.9.49': ('camellia-256-ctr', 'CAMELLIA-256-CTR'),
    '0.3.4401.5.3.1.9.50': ('camellia-256-cmac', 'CAMELLIA-256-CMAC'),
    '0.9': ('data', ),
    '0.9.2342': ('pss', ),
    '0.9.2342.19200300': ('ucl', ),
    '0.9.2342.19200300.100': ('pilot', ),
    '0.9.2342.19200300.100.1': ('pilotAttributeType', ),
    '0.9.2342.19200300.100.1.1': ('userId', 'UID'),
    '0.9.2342.19200300.100.1.2': ('textEncodedORAddress', ),
    '0.9.2342.19200300.100.1.3': ('rfc822Mailbox', 'mail'),
    '0.9.2342.19200300.100.1.4': ('info', ),
    '0.9.2342.19200300.100.1.5': ('favouriteDrink', ),
    '0.9.2342.19200300.100.1.6': ('roomNumber', ),
    '0.9.2342.19200300.100.1.7': ('photo', ),
    '0.9.2342.19200300.100.1.8': ('userClass', ),