Improve Beagleconnect docs

Completely revamp beagleconnect technology page.

• Sperate the actual theory from demos
• Add new graphics. My UI/UX sense is well not great, so someone else should probably improve them later, but this should at least provide a starting point
• Does not contain the demo docs for BeaglePlay + Bcf yet (just points to the old docs). This is mainly due to the fact that even if we add them right now, they will not work. I am working on migrating both greybus-node and greybus-host stuff to build against upstream (and merge them to a single greybus-for-zephyr module) but well it is dependent on how fast stuff moves in repos outside of my control.

The docs on BeagleConnect Technology are sorely lacking right now. This is an attempt to provide the bare essentials.

Signed-off-by: Ayush Singh ayushdevel1325@gmail.com