perf(cache): pgx pool connector (#8703)

# Which Problems Are Solved

Cache implementation using a PGX connection pool.

# How the Problems Are Solved

Defines a new schema `cache` in the zitadel database.
A table for string keys and a table for objects is defined.
For postgreSQL, tables are unlogged and partitioned by cache name for
performance.

Cockroach does not have unlogged tables and partitioning is an
enterprise feature that uses alternative syntax combined with sharding.
Regular tables are used here.

# Additional Changes

- `postgres.Config` can return a pxg pool. See following discussion

# Additional Context

- Part of https://github.com/zitadel/zitadel/issues/8648
- Closes https://github.com/zitadel/zitadel/issues/8647

---------

Co-authored-by: Silvan <silvan.reusser@gmail.com>

internal/database/postgres/pg.go

@@ -72,15 +72,15 @@ func (_ *Config) Decode(configs []interface{}) (dialect.Connector, error) {
 	return connector, nil
 }
 
-func (c *Config) Connect(useAdmin bool, pusherRatio, spoolerRatio float64, purpose dialect.DBPurpose) (*sql.DB, error) {
+func (c *Config) Connect(useAdmin bool, pusherRatio, spoolerRatio float64, purpose dialect.DBPurpose) (*sql.DB, *pgxpool.Pool, error) {
 	connConfig, err := dialect.NewConnectionConfig(c.MaxOpenConns, c.MaxIdleConns, pusherRatio, spoolerRatio, purpose)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
 	config, err := pgxpool.ParseConfig(c.String(useAdmin, purpose.AppName()))
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
 	if connConfig.MaxOpenConns != 0 {
@@ -95,14 +95,14 @@ func (c *Config) Connect(useAdmin bool, pusherRatio, spoolerRatio float64, purpo
 		config,
 	)
 	if err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
 	if err := pool.Ping(context.Background()); err != nil {
-		return nil, err
+		return nil, nil, err
 	}
 
-	return stdlib.OpenDBFromPool(pool), nil
+	return stdlib.OpenDBFromPool(pool), pool, nil
 }
 
 func (c *Config) DatabaseName() string {