Implement /swiss/{id}.trf endpoint

[Anupya]

Description

• Implement /swiss/{id}.trf
  • I am not sure how to define a return type TRF (as it is not JSON formattable), so the endpoint's return type will be str.
  • This is the reason I did not include a test as the API endpoint does not return JSON.

After merge

Check off /swiss/{id}.trf in #6.

Checklist

Checklist when adding a new endpoint

• Added new endpoint to the README.md
• Ensure that my endpoint name does not repeat the name of the client. Wrong: client.users.get_user(), Correct: client.users.get()
• Typed the returned JSON using TypedDicts in berserk/types/, example <--not returning JSON so not relevant
• Tested GET endpoints not requiring authentification. Documentation, example <--not returning JSON so not relevant
• Added the endpoint and your name to CHANGELOG.md in the To be released section (to be created if necessary) <--leaving it up to the maintainer