fix(eventstore): use decimal, correct mirror (#9914)

# Eventstore fixes

- `event.Position` used float64 before which can lead to [precision
loss](https://github.com/golang/go/issues/47300). The type got replaced
by [a type without precision
loss](https://github.com/jackc/pgx-shopspring-decimal)
- the handler reported the wrong error if the current state was updated
and therefore took longer to retry failed events.

# Mirror fixes

- max age of auth requests can be configured to speed up copying data
from `auth.auth_requests` table. Auth requests last updated before the
set age will be ignored. Default is 1 month
- notification projections are skipped because notifications should be
sent by the source system. The projections are set to the latest
position
- ensure that mirror can be executed multiple times

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

internal/database/database.go

@@ -64,6 +64,10 @@ func CloseTransaction(tx Tx, err error) error {
 	return commitErr
 }
 
+const (
+	PgUniqueConstraintErrorCode = "23505"
+)
+
 type Config struct {
 	Dialects  map[string]interface{} `mapstructure:",remain"`
 	connector dialect.Connector