add a runbook for payment latency alerts

Author: arikalon1

docs/how-it-works/HighPaymentsRequestsLatency.rst

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+Troubleshooting runbook: HighPaymentsRequestsLatency
+##################################################
+
+This alert fires when there's a high latency on the payment request microservice
+
+Troubleshooting steps
+----------------------
+
+1. Check the pods the alert is fired on for errors
+2. Check that the `supabase` pod on the cluster is up and running properly. It's used to store and get payment requests.
+   If the `supabase` db is unhealthy, this is probably the cause for it. For this, contact the DB INFRA team
+3. Check account-config workload. It's also used on the payment requests flow. For errors in this workload, contact the `config management` application team
+
+If any of the above has error, this is most likely the issue