Add a page to configure radioconf to ap admin mode

[mc-hamster]

Add a page /admin to perform some common configuration changes.

Include:

• Wifi Client Credentials & Mode
• ~~Always Powered~~
• Smart Position Update
• what else?

Save with: nodeDB.saveToDisk()

Note: Anyone reading this may propose additional preferences in the comments below.

[Noki]

• Region
• Uplink/Downlink enabled
• ~~Is Router~~

and maybe the store and forward plugin

[sachaw]

Out of scope, webui/cli/apps/etc will handle these