Container feature detection

There are an increasing set of features which are:

• not in the spec
• required in practice for all production homeservers.

A few examples:

• ability to delete media.
• ability to delete rooms/history entirely.
• change rate limits for the CS API.

It would be nice if a homeserver could "declare" that it supports this, which then runs some magic command on the container to enable/disable this in the container prior to startup (to avoid needing to SIGHUP a running container or other nonsense). If this declaration API is standardised, it would allow the same rate limit tests to work across different HSes for example, and if not, it can be easily skipped.

This has overlap with https://github.com/matrix-org/complement/issues/654 which suggests a configuration format for saying which tests should be run. One can imagine that the "rate limit tests" were an MSC and hence could be opted-in to. The difference is that this needs configuration on a per-test basis, as we usually want very high rate limits in tests.

Empieza comparando esta propuesta con Complement issue 654, especialmente con el formato de configuración sugerido. Define cómo un homeserver declara la compatibilidad con las funcionalidades y cómo esa declaración habilita u omite pruebas individuales antes de iniciar el contenedor. Se considera terminado cuando el enfoque cubre ejemplos como la eliminación de medios, la eliminación de salas/historial y los límites de velocidad por prueba, sin requerir reiniciar un contenedor en ejecución.