Fulltext implementation using Bleve (#2675)

Based on #2480

This actually indexes events based on their event type. They are removed
from the index if we receive a `m.room.redaction` event on the
`OutputRoomEvent` stream.
An admin endpoint is added to reindex all existing events.


Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>

cmd/generate-config/main.go

@@ -5,10 +5,11 @@ import (
 	"fmt"
 	"path/filepath"
 
-	"github.com/matrix-org/dendrite/setup/config"
 	"github.com/matrix-org/gomatrixserverlib"
 	"golang.org/x/crypto/bcrypt"
 	"gopkg.in/yaml.v2"
+
+	"github.com/matrix-org/dendrite/setup/config"
 )
 
 func main() {
@@ -82,6 +83,12 @@ func main() {
 				EnableInbound:  true,
 				EnableOutbound: true,
 			}
+			cfg.SyncAPI.Fulltext = config.Fulltext{
+				Enabled:   true,
+				IndexPath: config.Path(filepath.Join(*dirPath, "fulltextindex")),
+				InMemory:  true,
+				Language:  "en",
+			}
 		}
 	} else {
 		var err error