Add endpoint to serve all FT balances and native NEAR balance together

[telezhnaya]

We dropped the "Coins" category, now we have "NEAR" and "FT". We no longer have the endpoint to have all the available balances, the users have to have 2 requests, one for native NEAR balance, and one for FT balances.
I want to return such an endpoint back.

The hardest part here is to design the tags so that Swagger can show the endpoints in a logical way.

Ideally, I want to have nested tags with the following structure:

Balances:
    FT:
        ...
    NFT:
        ...
    NEAR:
       ...
    get_balances() <- new endpoint in the root of the tag
Transactions:
    ...

Now the tags are flat, it looks this way: