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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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if backend == 'pyopenssl':
            if not PYOPENSSL_FOUND:
                module.fail_json(msg=missing_required_lib('pyOpenSSL >= {0}'.format(MINIMAL_PYOPENSSL_VERSION)),
                                 exception=PYOPENSSL_IMP_ERR)
            module.deprecate('The module is using the PyOpenSSL backend. This backend has been deprecated', version='2.13')
            private_key = PrivateKeyPyOpenSSL(module)
        elif backend == 'cryptography':
            if not CRYPTOGRAPHY_FOUND:
                module.fail_json(msg=missing_required_lib('cryptography >= {0}'.format(MINIMAL_CRYPTOGRAPHY_VERSION)),
                                 exception=CRYPTOGRAPHY_IMP_ERR)
            private_key = PrivateKeyCryptography(module)
        if private_key.state == 'present':
            if module.check_mode:
                result = private_key.dump()
                result['changed'] = module.params['force'] or not private_key.check(module)
                module.exit_json(**result)
            private_key.generate(module)
        else:
            if module.check_mode:
                result = private_key.dump()
                result['changed'] = os.path.exists(module.params['path'])
                module.exit_json(**result)
            private_key.remove(module)
        result = private_key.dump()
        module.exit_json(**result)
    except crypto_utils.OpenSSLObjectError as exc:
        module.fail_json(msg=to_native(exc))
if __name__ == '__main__':
    main()