[djangoflow_emoji_rain] Add Controller for Rain Control

[adar2378]

Description: Provide a controller that allows users to start and stop the rain animation at will. This feature adds user control over the rain effect, making it more interactive.

Implementation: Create a controller class that manages the animation and exposes methods like startRain() and stopRain(). Users can use these methods to control when the rain animation begins and ends.

Controller API Documentation:

Description: As part of this enhancement, ensure that the controller's API is well-documented in the package documentation. This will guide users on how to use the controller effectively.

Implementation: Update the package's documentation to include a section on the new controller class. Provide examples and clear explanations of how to use it to control the rain animation.