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

cmd/setup/setup.go

@@ -165,6 +165,7 @@ func Setup(ctx context.Context, config *Config, steps *Steps, masterKey string)
 	steps.s33SMSConfigs3TwilioAddVerifyServiceSid = &SMSConfigs3TwilioAddVerifyServiceSid{dbClient: esPusherDBClient}
 	steps.s34AddCacheSchema = &AddCacheSchema{dbClient: queryDBClient}
 	steps.s35AddPositionToIndexEsWm = &AddPositionToIndexEsWm{dbClient: esPusherDBClient}
+	steps.s36FillV2Milestones = &FillV2Milestones{dbClient: queryDBClient, eventstore: eventstoreClient}
 
 	err = projection.Create(ctx, projectionDBClient, eventstoreClient, config.Projections, nil, nil, nil)
 	logging.OnError(err).Fatal("unable to start projections")
@@ -209,6 +210,7 @@ func Setup(ctx context.Context, config *Config, steps *Steps, masterKey string)
 		steps.s30FillFieldsForOrgDomainVerified,
 		steps.s34AddCacheSchema,
 		steps.s35AddPositionToIndexEsWm,
+		steps.s36FillV2Milestones,
 	} {
 		mustExecuteMigration(ctx, eventstoreClient, step, "migration failed")
 	}
@@ -390,6 +392,7 @@ func initProjections(
 	}
 	commands, err := command.StartCommands(
 		eventstoreClient,
+		config.Caches,
 		config.SystemDefaults,
 		config.InternalAuthZ.RolePermissionMappings,
 		staticStorage,