fix(eventstore): use decimal, correct mirror (#9916)

# 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

internal/eventstore/repository/mock/repository.mock.impl.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/shopspring/decimal"
 	"github.com/stretchr/testify/assert"
 	"go.uber.org/mock/gomock"
 
@@ -197,8 +198,8 @@ func (e *mockEvent) Sequence() uint64 {
 	return e.sequence
 }
 
-func (e *mockEvent) Position() float64 {
-	return 0
+func (e *mockEvent) Position() decimal.Decimal {
+	return decimal.Decimal{}
 }
 
 func (e *mockEvent) CreatedAt() time.Time {