WiFi: store/manage multiple connections

Follow-up of https://github.com/tiny-pilot/tinypilot/pull/1804. Note: at the time of this writing (2024-06-24) that feature is not yet implemented.

Currently, the WiFi feature is designed so that it allows to store a single WiFi connection. We could enhance the functionality so that users are able to store multiple WiFi networks. That might be useful, if the user carries around their TinyPilot device and uses it in different environments, because the device then could automatically connect to the respective WiFi.

One functionality that we may want to consider is that it’s technically possible to specify the priority of networks: the question is whether we want to offer that, though, because it’s more complex to build.

Start by reviewing pull request #1804, which this issue follows, to understand the existing single-connection WiFi feature. Define how multiple networks should be stored and selected for automatic connection, and resolve whether network priority is part of the scope. Done means users can store multiple networks and the device connects to the appropriate one in different environments.