Add endpoint to read firmware capabilities

[proddy]

Bring back the Features context in the Web and use this HTTP Get endpoint to bring back capabilities which we can use to determine behavior in the web pages. For example showing the TLS option in the MQTT settings only for ESP32's with larger flash sizes (>4MB) or WPA3 support on firmware compiled with IDF4.4.4 or extra options if the firmware is compiled with DEBUG, etc...

[proddy]

added to dev2. The features context only has two values in the json object (version & platform) which can be called from anywhere in the web code. We can extend later for other things we need to pull back from the firmware. This way we can set values in platformio.ini as -D defines and these will be identified in the web frontend.

[proddy]

To use, add:

import { FeaturesContext } from '../../contexts/features';
const { features } = useContext(FeaturesContext);

and then features holds the values.