2.2 Update Securing NATS

[ColinSullivan1]

Security Documentation

This could be under: https://github.com/nats-io/nats.docs/tree/master/nats-server/configuration/securing_nats.

If this documentation should be in a different place please comment here.

In a PR, please provide documentation to address:

• [ ] CIDR Block Checking
• [ ] Time Restrictions
• [ ] More JWT Usage Examples
• [ ] Additional Metadata (e.g descriptions)
• [ ] JetStream Account Options

For these sections, please make a note that these features apply to 2.2.

Under NATS Tools:

• [ ] JWT V2 (nsc)
• [ ] Default User Permissions (nsc)
• [ ] Auto Generate System Account (nsc)

Miscellaneous Server Configuration

• [ ] Subject Mapping and Bridging

Of course, add additional documentation as necessary.

/CC @gcolliso