bot: add an ability to use custom url builder

[d0ctr]

Same reasons as for #558, but a more robust solution as allows to use one of the setting's fields instead of two (URL and test env switcher)

[demget]

I don't like the URLBuilder name, and what's the use case of being able to pass it to the bot settings?

[d0ctr]

I don't like the URLBuilder name, and what's the use case of being able to pass it to the bot settings?

Telegram servers have a test environment, that has a different path: <base>/bot<token>/test/<method>. The name can be whatever you want, but without the builder or a special option the test environment is inaccessible.

[demget]

For testing purposes, I'll merge #558.