Move high-level architecture doc to this repo

[llucax]

We have this in the SDK from the times we thought the dispatch interface will go to the SDK:

• https://github.com/frequenz-floss/frequenz-sdk-python/wiki/Dispatching-Service

But I'm not a 100% sure if to this repo or to https://github.com/frequenz-floss/frequenz-api-dispatch/, and in any case where exactly to put it in the repo. Maybe we can have a new section in the docs with technical docs, or architecture.

FYI @frequenz-floss/api-dispatch-team

[Marenz]

I feel if it's more than just client stuff, api-dispatch might be better suited?

[llucax]

Yeah, not sure, I also feel that strictly speaking probably api-dispatch is more suitable, but thinking about users, I think probably no user will ever look into that repo, this will be the entry-point for users, and it might be good for users to know how dispatch works.

Sort of the same with the microgrid documentation, we have most of it in the SDK, not in api-microgrid. But still I'm not a 100% sure, just more inclined to put it here than in api-dispatch.

[Marenz]

Maybe we can have a less detailed overview for the user side in the client repos?

[llucax]

What would you remove?