Add audit doc (#732)

* doc: add auditlog docs, initial review

* doc: add path to redirect map

* fix: remove from redirect

* doc: update audit command

Author: Muni10

docs/persistence/postgres/how-to/enable-auditing.md

@@ -0,0 +1,51 @@
+---
+tags: [postgres, audit, troubleshooting, how-to]
+---
+
+# Audit logging
+
+!!! info "Only available for postgreSQL in GCP"
+
+    The cli used for this configuration can only detect sql instances in GCP.
+
+This guide describes how to enable audit logging in your postgreSQL database.
+
+The following steps need to be taken to enable the logging.
+
+1. [Configure database flags](#configure-database-flags-for-your-sql-instance), and configure replication etc.
+2. [Configure database internals](#use-the-nais-cli-to-configure-database-internals) to be the primary.
+
+For more information on audit logging, see the [official documentation](https://cloud.google.com/sql/docs/postgres/pg-audit).
+
+## Configure database flags for your sql instance
+
+```text
+$ cloudsql.enable_pgaudit = on
+$ pgaudit = read | write | all
+```
+
+Example application spec: 
+
+```yaml
+spec:
+  gcp:
+    sqlInstances:
+    - name: myapp
+      flags:
+        - name: "cloudsql.enable_pgaudit"
+          value: "on"
+        - name: "pgaudit.log"
+          value: "write"
+```
+
+## Use the nais cli to configure database internals
+
+The nais cli can be used to configure the database internals. This will fail if the necessary database flags have not been configured.
+The cli will log on to your database and create the pgaudit extension and also disable logging for the application user.
+
+```shell
+$ nais postgres enable-audit <application> <namespace> <context>
+```
+The application is required, the current namespace and context will be used if these are not specified.
+
+For more information on the nais cli, see the [official documentation](https://doc.nais.io/cli).