Introduce shared mutable context between update handlers

[tuscen]

What do you think of the idea making update handlers more like middlewares is ASP.NET Core which share mutable context instance? That way there could be a common session middleware (e.g. with separate storages for a chat and a user). Or a middleware that constructs ClaimsPrincipal and attaches it to the context instance. It would open possibilities to leverage existing packages from ASP.NET Core that aren't tied to HttpContext or HTTP in general like Authorization.

[tuscen]

Upon thinking about this there should be actual middlewares like in ASP.NET Core to properly manage this shared context. So they can cleanup after themeselves after each subsequent middleware invocation. Though I do not know how well this concept of middlewares fits with bots.