refactor: consolidate database pools (#9105)

# Which Problems Are Solved

Zitadel currently uses 3 database pool, 1 for queries, 1 for pushing
events and 1 for scheduled projection updates. This defeats the purpose
of a connection pool which already handles multiple connections.

During load tests we found that the current structure of connection
pools consumes a lot of database resources. The resource usage dropped
after we reduced the amount of database pools to 1 because existing
connections can be used more efficiently.

# How the Problems Are Solved

Removed logic to handle multiple connection pools and use a single one.

# Additional Changes

none

# Additional Context

part of https://github.com/zitadel/zitadel/issues/8352

internal/database/dialect/config.go

@@ -26,36 +26,11 @@ type Matcher interface {
 }
 
 const (
-	QueryAppName             = "zitadel_queries"
-	EventstorePusherAppName  = "zitadel_es_pusher"
-	ProjectionSpoolerAppName = "zitadel_projection_spooler"
-	defaultAppName           = "zitadel"
+	DefaultAppName = "zitadel"
 )
 
-// DBPurpose is what the resulting connection pool is used for.
-type DBPurpose int
-
-const (
-	DBPurposeQuery DBPurpose = iota
-	DBPurposeEventPusher
-	DBPurposeProjectionSpooler
-)
-
-func (p DBPurpose) AppName() string {
-	switch p {
-	case DBPurposeQuery:
-		return QueryAppName
-	case DBPurposeEventPusher:
-		return EventstorePusherAppName
-	case DBPurposeProjectionSpooler:
-		return ProjectionSpoolerAppName
-	default:
-		return defaultAppName
-	}
-}
-
 type Connector interface {
-	Connect(useAdmin bool, pusherRatio, spoolerRatio float64, purpose DBPurpose) (*sql.DB, *pgxpool.Pool, error)
+	Connect(useAdmin bool) (*sql.DB, *pgxpool.Pool, error)
 	Password() string
 	Database
 }