* Add support for MSC3916

* Add changelog

* Add tests for preview_url and config authenticated endpoints

* Add placeholder tests for downloads and thumbnails

* Test X-Matrix auth header stuff

* Validate signing keys more correctly

* Add early documentation for what this setup will look like

* Fix imports

* Update tests

* Add resolvematrix.dev tests

* Fix URL preview test

* Support receiving `/versions` and enabling MSC3916 support

* Remove placeholder docs

* Make outbound federation requests using MSC3916

* Validate X-Matrix destination correctly

* Factor out signing key generation

* Allow overriding the auth header in tests

* Print signing key path when printing domains

* Configure test MMR instances with a signing key

* Allow lazy ServeFile implementations

* Add federation download test

* Re-add merge conflicts in changelog

* Support http-only federation for tests

* Strip Go-added URI segments

* Fix test shutdown

* Remove unused test

* Enable failing tests

* Ensure signing keys exist inside container

* Fix signing key alignment between dependencies

* Ensure signing key information is carried into the config object

* Generally treat homeserver config a bite more safely

* Support and use new 3916v2 federation download URL

* Fix signing key permissions?

* Fix routing

* Update redirect-supporting behaviour

* Support redirects

* Finish tests

* Mark test function as deprecated to discourage use

* Avoid testcontainers tests from overwriting the config concurrently.

* host.docker.internal doesn't exist on linux

* Temporarily disable upload tests

* Support federation thumbnails again

* Fix tests for auth header

* Switch to stable endpoints

* Maybe use the correct stable endpoint too

* Revert "Temporarily disable upload tests"

This reverts commit e21fa0135b8fa880af7bbb7690e147a12946c28e.

* Try fixing tests

* Hardcode `host.docker.internal` again

* Fix redirect behaviour on federation

* Move endpoints to correct package

* Maybe remove the dev code