Add config option to disable discovery

[jmbrunskill]

Fixes #5018

👩🏻‍💻 What does this PR do?

Adds a new option you can put in your local.yaml file to turn on/off discovery.

The default Auto will disable discovery in Debug Build (normal workflow for devs)

server:
    discovery: Auto 

server:
    discovery: Enabled 

server:
    discovery: Disabled

💌 Any notes for the reviewer?

Haven't removed my old catch_panic_unwind code in this PR, should I?

🧪 Testing

• Start server in the office see if we get any crashes due to astro-dns in Auto mode
• Check you can turn on the discovery service with discovery: Enabled
• Check that discovery works correctly in Window RC Build for 2.6 (When available)

📃 Documentation

• Part of an epic: documentation will be completed for the feature as a whole
• No documentation required: no user facing changes or a bug fix which isn't a change in behaviour
• These areas should be updated or checked:
  1.
  2.

[andreievg]

Thanks @jmbrunskill, look good, as per out discussion, may need a little bit of tweaking. We in dev atm so happy with it as is or with those small tweaks after this approval