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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`

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        version_added: "2.8"
    force:
        description:
            - Should the key be regenerated even if it already exists.
        type: bool
        default: no
    path:
        description:
            - Name of the file in which the generated TLS/SSL private key will be written. It will have 0600 mode.
        type: path
        required: true
    passphrase:
        description:
            - The passphrase for the private key.
        type: str
        version_added: "2.4"
    cipher:
        description:
            - The cipher to encrypt the private key. (Valid values can be found by
              running `openssl list -cipher-algorithms` or `openssl list-cipher-algorithms`,
              depending on your OpenSSL version.)
            - When using the C(cryptography) backend, use C(auto).
        type: str
        version_added: "2.4"
    select_crypto_backend:
        description: