feat(eventstore): increase parallel write capabilities (#5940)

This implementation increases parallel write capabilities of the eventstore.
Please have a look at the technical advisories: [05](https://zitadel.com/docs/support/advisory/a10005) and  [06](https://zitadel.com/docs/support/advisory/a10006).
The implementation of eventstore.push is rewritten and stored events are migrated to a new table `eventstore.events2`.
If you are using cockroach: make sure that the database user of ZITADEL has `VIEWACTIVITY` grant. This is used to query events.

internal/eventstore/handler/v2/mock_test.go

@@ -0,0 +1,18 @@
+package handler
+
+var _ Projection = (*projection)(nil)
+
+type projection struct {
+	name     string
+	reducers []AggregateReducer
+}
+
+// Name implements Projection
+func (p *projection) Name() string {
+	return p.name
+}
+
+// Reducers implements Projection
+func (p *projection) Reducers() []AggregateReducer {
+	return p.reducers
+}