feat(api): implement MSC4143 RTC transports discovery endpoint

Add dedicated \`GET /_matrix/client/v1/rtc/transports\` and \`GET /_matrix/client/unstable/org.matrix.msc4143/rtc/transports\` endpoints for MatrixRTC focus discovery (MSC4143), replacing the deprecated well-known approach.

Move RTC foci configuration from \`[global.well_known]\` into a new \`[global.matrix_rtc]\` config section with a \`foci\` field. Remove \`rtc_foci\` from the \`.well-known/matrix/client\` response. Update LiveKit setup documentation accordingly.

Closes #1431

conduwuit-example.toml

@@ -1844,17 +1844,6 @@
 #
 #support_mxid =
 
-# A list of MatrixRTC foci URLs which will be served as part of the
-# MSC4143 client endpoint at /.well-known/matrix/client.  If you're
-# setting up livekit, you'd want something like:
-# rtc_focus_server_urls = [
-#     { type = "livekit", livekit_service_url = "https://livekit.example.com" },
-# ]
-#
-# To disable, set this to be an empty vector (`[]`).
-#
-#rtc_focus_server_urls = []
-
 [global.blurhashing]
 
 # blurhashing x component, 4 is recommended by https://blurha.sh/
@@ -1873,6 +1862,23 @@
 #
 #blurhash_max_raw_size = 33554432
 
+[global.matrix_rtc]
+
+# A list of MatrixRTC foci (transports) which will be served via the
+# MSC4143 RTC transports endpoint at
+# `/_matrix/client/v1/rtc/transports`. If you're setting up livekit,
+# you'd want something like:
+# ```toml
+# [global.matrix_rtc]
+# foci = [
+#     { type = "livekit", livekit_service_url = "https://livekit.example.com" },
+# ]
+# ```
+#
+# To disable, set this to an empty list (`[]`).
+#
+#foci = []
+
 [global.ldap]
 
 # Whether to enable LDAP login.