Implement AvailableOpponents Controller

[Atralupus]

Create a REST API controller, AvailableOpponentController,
This controller should enable users to fetch their opponent list and allow resetting the list for a specific interval.

1. Implement a GetAvailableOpponents endpoint:

   • Route: GET /season/{seasonId}/available-opponents
   • Fetch and return a list of opponents.

2. Implement a ResetOpponents endpoint:

   • Route: POST /season/{seasonId}/available-opponents
   • Trigger a reset for the opponents list.

Notes

• The interval resets are handled by a separate worker.

• Opponents should be grouped and filtered based on rank ranges as per the provided specification:

  Group      Range (as percentage of user’s rank)
  -----------------------------------------------
  Upper 1    20–40%
  Upper 2    40–80%
  Same Rank  80–120%
  Lower 1    120–180%
  Lower 2    180–300%
  

  The endpoint should fetch and return opponents grouped without calculating scores.