perf(milestones): refactor (#8788)

# Which Problems Are Solved

Milestones used existing events from a number of aggregates. OIDC
session is one of them. We noticed in load-tests that the reduction of
the oidc_session.added event into the milestone projection is a costly
business with payload based conditionals. A milestone is reached once,
but even then we remain subscribed to the OIDC events. This requires the
projections.current_states to be updated continuously.


# How the Problems Are Solved

The milestone creation is refactored to use dedicated events instead.
The command side decides when a milestone is reached and creates the
reached event once for each milestone when required.

# Additional Changes

In order to prevent reached milestones being created twice, a migration
script is provided. When the old `projections.milestones` table exist,
the state is read from there and `v2` milestone aggregate events are
created, with the original reached and pushed dates.

# Additional Context

- Closes https://github.com/zitadel/zitadel/issues/8800

internal/api/authz/instance.go

@@ -114,7 +114,15 @@ func WithConsole(ctx context.Context, projectID, appID string) context.Context {
 
 	i.projectID = projectID
 	i.appID = appID
-	//i.clientID = clientID
+	return context.WithValue(ctx, instanceKey, i)
+}
+
+func WithConsoleClientID(ctx context.Context, clientID string) context.Context {
+	i, ok := ctx.Value(instanceKey).(*instance)
+	if !ok {
+		i = new(instance)
+	}
+	i.clientID = clientID
 	return context.WithValue(ctx, instanceKey, i)
 }