[TestBot] Configure different controllers for each type of bot

[ParadoxARG]

Describe the solution you'd like

The TestBot has three possible bot configuration (EchoBot, DialogsBot, and DialogsAndWelcomeBot). The bot behavior is defined by an environment variable called chosenBot (see configuration).
We should have three different controllers, one for each type of bot, so when the user wants to use one type of behavior he just needs to connect to that bot's endpoint. With this change, the user will be able to use all the three types of bot without any change in the project configuration.

Describe alternatives you've considered

Create one controller for each type of Bot and make them available as different endpoints.

[enhancement]