Reorganize config into sections, allow tracing filters to be changed at runtime

Config changes:

old	new
turn_username	turn.username
turn_password	turn.password
turn_uris	turn.uris
turn_secret	turn.secret
turn_ttl	turn.ttl
database_backend	database.backend
database_path	database.path
db_cache_capacity_mb	database.cache_capacity_mb
rocksdb_max_open_files	database.rocksdb_max_open_files
allow_prometheus	observability.metrics.enable
allow_jaeger	observability.traces.enable
-	observability.traces.filter
-	observability.traces.endpoint
tracing_flame	observability.flame.enable
-	observability.flame.filter
-	observability.flame.filename
log	observability.logs.filter
log_colors	observability.logs.colors
log_format	observability.logs.format
-	observability.logs.timestamp
allow_federation	federation.enable
trusted_servers	federation.trusted_servers
max_fetch_prev_events	federation.max_fetch_prev_events
max_concurrent_requests	federation.max_concurrent_requests