Initial Store & Forward Implementation (#2917)

This adds store & forward relays into dendrite for p2p.
A few things have changed:
- new relay api serves new http endpoints for s&f federation
- updated outbound federation queueing which will attempt to forward
using s&f if appropriate
- database entries to track s&f relays for other nodes

relayapi/storage/sqlite3/storage.go

@@ -0,0 +1,64 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sqlite3
+
+import (
+	"database/sql"
+
+	"github.com/matrix-org/dendrite/internal/caching"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/relayapi/storage/shared"
+	"github.com/matrix-org/dendrite/setup/base"
+	"github.com/matrix-org/dendrite/setup/config"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+// Database stores information needed by the federation sender
+type Database struct {
+	shared.Database
+	db     *sql.DB
+	writer sqlutil.Writer
+}
+
+// NewDatabase opens a new database
+func NewDatabase(
+	base *base.BaseDendrite,
+	dbProperties *config.DatabaseOptions,
+	cache caching.FederationCache,
+	isLocalServerName func(gomatrixserverlib.ServerName) bool,
+) (*Database, error) {
+	var d Database
+	var err error
+	if d.db, d.writer, err = base.DatabaseConnection(dbProperties, sqlutil.NewExclusiveWriter()); err != nil {
+		return nil, err
+	}
+	queue, err := NewSQLiteRelayQueueTable(d.db)
+	if err != nil {
+		return nil, err
+	}
+	queueJSON, err := NewSQLiteRelayQueueJSONTable(d.db)
+	if err != nil {
+		return nil, err
+	}
+	d.Database = shared.Database{
+		DB:                d.db,
+		IsLocalServerName: isLocalServerName,
+		Cache:             cache,
+		Writer:            d.writer,
+		RelayQueue:        queue,
+		RelayQueueJSON:    queueJSON,
+	}
+	return &d, nil
+}