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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 -->

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    '1.2.643.2.2.20.3': ('id-GostR3410-94-b', ),
    '1.2.643.2.2.20.4': ('id-GostR3410-94-bBis', ),
    '1.2.643.2.2.21': ('GOST 28147-89', 'gost89'),
    '1.2.643.2.2.22': ('GOST 28147-89 MAC', 'gost-mac'),
    '1.2.643.2.2.23': ('GOST R 34.11-94 PRF', 'prf-gostr3411-94'),
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