Code Insights: Add documentation about insight loading and FE arch in general

Created by: vovakulikov

Since a really fast-growing amount of new functionality and constantly changing code-base, we stumbled over a lack of documentation. I suspect that this problem would lead us to the situation when nobody knows about all aspects and details in the code insights code-base. Also, this increases the lottery (bus) factor. Obviously, all these things are not good and we have to be worried about this.

My proposal here would be to сapture and describe all important historical decisions on the front end and provide some info about why we came up with something and didn’t with other possible solutions.