Matching Service: Cancel Matching Request

# Matching Service: Cancel Matching Request

## What to Do
- Allow users to **terminate their matching request** at any time before a match.
- On termination:
  - Remove user from the matching queue immediately.

## References
- Product Backlog: [FR6.3, FR6.3.1](https://docs.google.com/document/d/1DokYROrrlD4HXa1iXcaYqqO_ToTkWOkmm1tGLKdOSU4/edit?usp=sharing)
