Ensure that SSL CA is not required, is formatted correctly, and has a tooltip

[seanstory]

Part of #2438

This adds

  "required": False,
  "display": "textarea",
  "tooltip": "Specifies the root certificate from the Certificate Authority. The value of the certificate is used to validate the certificate presented by the <service type> server.",

to all ssl_ca RCF fields for all our connectors.

Checklists

Pre-Review Checklist

• this PR does NOT contain credentials of any kind, such as API keys or username/passwords (double check config.yml.example)
• this PR has a meaningful title
• this PR links to all relevant github issues that it fixes or partially addresses
• this PR has a thorough description
• Covered the changes with automated tests
• Tested the changes locally
• Added a label for each target release version (example: v7.13.2, v7.14.0, v8.0.0)
• Considered corresponding documentation changes
• if you added or changed Rich Configurable Fields for a Native Connector, you made a corresponding PR in Kibana

Related Pull Requests

• Kibana PR for native connectors: TODO
• docs PR to note optional nature: TODO

Release Note

Allows connectors that optionally may enable SSL to not require a certificate to be specified. Previously, this was only optional for Mongodb, but all other connectors required a cert if ssl was enabled.