Config value http_client_handler to support runtime resolving (via a callable maybe)

[lezhnev74]

I am using Laravel and want to customize the http client used by the package.
Config value http_client_handler allows only in-place instantiation like new MyHandler() as at the config loading step the container has not finished loading all the dependencies.

My point is that I need to configure the client at run-time, upon using Telegram bot.

So far my ideas:

• make config value http_client_handler to accept callable to resolve the client later at runtime
• remove final from BotsManager so I can override its behaviour to resolve client at runtime
• maybe something else?

p.s. within BotsManager config dependencies are resolved as new Api(...) so no opportunity to inject another implementation via the container.

I would be grateful for any clues on how to swap the http client at runtime?

[lezhnev74]

forked with this patch for now:
lezhnev74@2a0079c