Add docs for NATS authorization

[welteki]

Description

Update the JetStream page and recommended OpenFaaS Pro values for the new NATS authentication support.

Motivation and Context

• I have raised an issue to propose this change (required)

Document support for NATS authentication.

How Has This Been Tested?

• Verified the modified pages render correctly.
• Tested command examples.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have signed-off my commits with git commit -s