Security guide

[Hoverbear]

In https://github.com/timberio/vector/issues/1553 we added TLS to all applicable sources, and work to add this support to remaining sinks is ongoing.

As we discussed timberio/vector#2017 we noted that it would be of benefit to users if we did have a full guide for properly configuring TLS support.

Possible content:

• The right security for your deployment
• Understanding your threat model
• Configuration:
  • No security
  • Tokens + Plaintext (Authentication)
  • Pre-shared keys (Encryption)
  • mTLS (Authentication, Authorization, Encryption)
• Provisioning and configuration management tips

[dineshpalanivel]

@binarylogic Do we have the support for "Tokens+ Plaintext (AuthN)" for the source "syslog" at the moment? I have not see any pointers related to this in the documentation. Perhaps it will be great if we can further drill down the documentation to show what is supported on what sources.. Thoughts?