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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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- name: Generate an OpenSSL private key with the default values (4096 bits, RSA) and a passphrase
  openssl_privatekey:
    path: /etc/ssl/private/ansible.com.pem
    passphrase: ansible
    cipher: aes256
- name: Generate an OpenSSL private key with a different size (2048 bits)
  openssl_privatekey:
    path: /etc/ssl/private/ansible.com.pem
    size: 2048
- name: Force regenerate an OpenSSL private key if it already exists
  openssl_privatekey:
    path: /etc/ssl/private/ansible.com.pem
    force: yes
- name: Generate an OpenSSL private key with a different algorithm (DSA)
  openssl_privatekey:
    path: /etc/ssl/private/ansible.com.pem
    type: DSA
'''
RETURN = r'''
size:
    description: Size (in bits) of the TLS/SSL private key.
    returned: changed or success
    type: int
    sample: 4096
type:
    description: Algorithm used to generate the TLS/SSL private key.
    returned: changed or success
    type: str
    sample: RSA
curve: