Implement public rooms APIs (#185)

* Move events contents to common

* Basic database structure

* Complete database update

* Support visibility update and retrieval

* Add HTTP methods for visibility update and retrieval

* Add the database for the new component

* Add a listener for the new component

* Fix attribute update statements

* Create public rooms component

* Fix failing test

* Add roomserver consumer

* Fix a bug in aliases creation

* Add a check on type

* Implement public rooms directory

* Use auth API for visibility update

* Support filtering

* Add component to monolith

* Various fixes

* Fix computation of next public rooms batch

* Retrieve state events from the roomserver query API + avoid dupes on join

* Split update of string or boolean attribute in two separate functions

* Use event type to detect duplicate joins

* Improve the joined members counter computation

* Use event.RoomID()

src/github.com/matrix-org/dendrite/common/config/config.go

@@ -133,6 +133,9 @@ type Dendrite struct {
 		// The FederationSender database stores information used by the FederationSender
 		// It is only accessed by the FederationSender.
 		FederationSender DataSource `yaml:"federation_sender"`
+		// The PublicRoomsAPI database stores information used to compute the public
+		// room directory. It is only accessed by the PublicRoomsAPI server.
+		PublicRoomsAPI DataSource `yaml:"public_rooms_api"`
 	} `yaml:"database"`
 
 	// The internal addresses the components will listen on.
@@ -144,6 +147,7 @@ type Dendrite struct {
 		SyncAPI          Address `yaml:"sync_api"`
 		RoomServer       Address `yaml:"room_server"`
 		FederationSender Address `yaml:"federation_sender"`
+		PublicRoomsAPI   Address `yaml:"public_rooms_api"`
 	} `yaml:"listen"`
 }