[Feature] Support changing OpenShock server at runtime

[redmushie]

Pre-submission checklist

• [X] I checked that there is no other Feature Request describing my wish.
• [X] I checked that this feature is, in fact, not supported.
• [X] I accept that this issue may be closed if any of the above are found to be untrue.

What should be possible that currently is not?

Cofiguring the OpenShock server that the firmware connects to should be modifiable at runtime, not compile time.

• Add serial command to change server
• Add (prefilled) text field with baked-in URL as default value

Other remarks

No response

[hhvrc]

Why is this necessary?

[redmushie]

Because self-hosting is a primary feature and currently we're hard baking shocklink.net into all binaries.

[hhvrc]

Due to this being a change being one that is done very rarely I will not be swapping it at runtime, but will implement it as a set-and-reboot procedure, setting it at runtime introduces alot of complexity

[redmushie]

At a glance, I don't think that wouldn't make sense if you're still on the captive portal, since no gateway connection or auth token was acquired yet.

After thinking on it for a bit, I'm of the opinion that the minimum viable is "set and apply after reboot". Rebooting the board the second you change it will:

1. Boot you out of the captive portal network (if changing it that way), and;
2. Mess with attempts at automating configuration, as the serial connection will probably be interrupted, or at the very least be spammed with a large quantity of irrelevant logs. (Though I admit that's usually of little significance.)

[hhvrc]

Implemented in #223