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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 -->

'2.23.42.5.0': ('set-policy-root', ),
    '2.23.42.7': ('certificate extensions', 'set-certExt'),
    '2.23.42.7.0': ('setCext-hashedRoot', ),
    '2.23.42.7.1': ('setCext-certType', ),
    '2.23.42.7.2': ('setCext-merchData', ),
    '2.23.42.7.3': ('setCext-cCertRequired', ),
    '2.23.42.7.4': ('setCext-tunneling', ),
    '2.23.42.7.5': ('setCext-setExt', ),
    '2.23.42.7.6': ('setCext-setQualf', ),
    '2.23.42.7.7': ('setCext-PGWYcapabilities', ),
    '2.23.42.7.8': ('setCext-TokenIdentifier', ),
    '2.23.42.7.9': ('setCext-Track2Data', ),
    '2.23.42.7.10': ('setCext-TokenType', ),
    '2.23.42.7.11': ('setCext-IssuerCapabilities', ),
    '2.23.42.8': ('set-brand', ),
    '2.23.42.8.1': ('set-brand-IATA-ATA', ),
    '2.23.42.8.4': ('set-brand-Visa', ),
    '2.23.42.8.5': ('set-brand-MasterCard', ),
    '2.23.42.8.30': ('set-brand-Diners', ),
    '2.23.42.8.34': ('set-brand-AmericanExpress', ),
    '2.23.42.8.35': ('set-brand-JCB', ),
    '2.23.42.8.6011': ('set-brand-Novus', ),
    '2.23.43': ('wap', ),
    '2.23.43.1': ('wap-wsg', ),
    '2.23.43.1.4': ('wap-wsg-idm-ecid', ),
    '2.23.43.1.4.1': ('wap-wsg-idm-ecid-wtls1', ),
    '2.23.43.1.4.3': ('wap-wsg-idm-ecid-wtls3', ),
    '2.23.43.1.4.4': ('wap-wsg-idm-ecid-wtls4', ),
    '2.23.43.1.4.5': ('wap-wsg-idm-ecid-wtls5', ),
    '2.23.43.1.4.6': ('wap-wsg-idm-ecid-wtls6', ),