Add a new component: currentstateserver (#1171)

* Add a new component: currentstateserver

- Add a skeleton for it, with databases and a single query method.
- Add integration tests for it.
- Add listen/address fields in the config (breaking as this will force people to specify this to validate)

Not currently hooked up to anything yet.

* Unbreak config tests

* Add current_state to sample config

* comments

currentstateserver/storage/sqlite3/storage.go

@@ -0,0 +1,39 @@
+package sqlite3
+
+import (
+	"database/sql"
+
+	"github.com/matrix-org/dendrite/currentstateserver/storage/shared"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+)
+
+type Database struct {
+	shared.Database
+	db *sql.DB
+	sqlutil.PartitionOffsetStatements
+}
+
+// NewDatabase creates a new sync server database
+// nolint: gocyclo
+func NewDatabase(dataSourceName string) (*Database, error) {
+	var d Database
+	cs, err := sqlutil.ParseFileURI(dataSourceName)
+	if err != nil {
+		return nil, err
+	}
+	if d.db, err = sqlutil.Open(sqlutil.SQLiteDriverName(), cs, nil); err != nil {
+		return nil, err
+	}
+	if err = d.PartitionOffsetStatements.Prepare(d.db, "currentstate"); err != nil {
+		return nil, err
+	}
+	currRoomState, err := NewSqliteCurrentRoomStateTable(d.db)
+	if err != nil {
+		return nil, err
+	}
+	d.Database = shared.Database{
+		DB:               d.db,
+		CurrentRoomState: currRoomState,
+	}
+	return &d, nil
+}