refactor(database): exchange connection pool (#8325)

# Which Problems Are Solved

The connection pool of go uses a high amount of database connections.

# How the Problems Are Solved

The standard lib connection pool was replaced by `pgxpool.Pool`

# Additional Changes

The `db.BeginTx`-spans are removed because they cause to much noise in
the traces.

# Additional Context

- part of https://github.com/zitadel/zitadel/issues/7639

internal/eventstore/v3/push.go

@@ -14,14 +14,11 @@ import (
 	"github.com/zitadel/logging"
 
 	"github.com/zitadel/zitadel/internal/eventstore"
-	"github.com/zitadel/zitadel/internal/telemetry/tracing"
 	"github.com/zitadel/zitadel/internal/zerrors"
 )
 
 func (es *Eventstore) Push(ctx context.Context, commands ...eventstore.Command) (events []eventstore.Event, err error) {
-	ctx, spanBeginTx := tracing.NewNamedSpan(ctx, "db.BeginTx")
 	tx, err := es.client.BeginTx(ctx, nil)
-	spanBeginTx.EndWithError(err)
 	if err != nil {
 		return nil, err
 	}