Sa/mspca 9 approve deny match and get all volunteers

[shreeyaadhikari]

ℹ️ Issue

Closes MSPCA-9

📝 Description

Adds the ability for foster coordinators to approve or deny pending matches, and to view a full list of volunteers regardless of their match status.

Briefly list the changes made to the code:

1. Added PATCH /matches/:matchId/approve which sets a match's status to COMPLETE.
2. Added PATCH /matches/:matchId/deny which sets a match's status to DENIED and stores a required, non-empty deniedReason on the match.
3. Added DenyMatchDto with @ IsNotEmpty()/@ IsString() validation so requests with a missing or empty reason are rejected with a 400 before reaching the service layer.
4. Added GET /volunteers which returns the full list of volunteers with no filtering, giving coordinators visibility into all volunteers regardless of match status.
5. Added validateId checks in MatchesController for both new endpoints, returning a 400 for invalid IDs and a 404 (via NotFoundException) when a match isn't found.
6. Added service and controller tests

✔️ Verification

Ran yarn test. All service and controller tests pass for MatchesService, MatchesController, VolunteersService and VolunteersController.