[48] Add Base WS's endpoint (aka BaseHTTPEndpoint)

[DmitryBurnaev]

• added base class-handler
• added bast test-class (with access to WS client)
• added new util (create asyncio task)

[dolamroth]

Можем ли мы использовать anyio вместо asyncio для create_task? https://anyio.readthedocs.io/en/stable/tasks.html