Remove authentication requirement for GET /_matrix/media/v3/config

[catfromplan9]

Title is pretty self explanatory. I feel like this info is not sensitive at all and it'd be useful to check this to decide if you want to use a server, because if its really low you might rather avoid signing up on that homeserver

[turt2live]

This is intentional, as it allows for per-user limits.

[catfromplan9]

This is intentional, as it allows for per-user limits.

Perhaps the server's default limit could be displayed instead?

[turt2live]

unauthenticated users don't need to know the limit :)