[feature] Implement stub `authorize_interaction` route (#4557)

Updates #4548

# Description

This PR implements a route for the `/authorize_interaction` endpoint. This endpoint is used when an interaction request comes from a remote Mastodon instance, e.g. when a user clicks on the reply button and enters their GoToSocial server address into the field.

closes #4548

## Checklist

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [x] I/we have made any necessary changes to documentation.
- [ ] I/we have added tests that cover new code.
- [ ] I/we have run tests and they pass locally with the changes.
- [ ] I/we have run `go fmt ./...` and `golangci-lint run`.

Co-authored-by: tobi <tobi.smethurst@protonmail.com>
Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4557
Co-authored-by: Kevin Gimbel <kevin@gimbel.dev>
Co-committed-by: Kevin Gimbel <kevin@gimbel.dev>

0 files changed, 0 insertions, 0 deletions