feat(coderd): add retention policy configuration (#21021)

Add `RetentionConfig` with server flags for configuring data retention:

- `--audit-logs-retention`: retention for audit log entries
- `--connection-logs-retention`: retention for connection logs
- `--api-keys-retention`: retention for expired API keys (default 7d)

Updates #20743

enterprise/cli/testdata/coder_server_--help.golden

@@ -697,6 +697,27 @@ updating, and deleting workspace resources.
           Number of provisioner daemons to create on start. If builds are stuck
           in queued state for a long time, consider increasing this.
 
+RETENTION OPTIONS: 
+Configure data retention policies for various database tables. Retention
+policies automatically purge old data to reduce database size and improve
+performance. Setting a retention duration to 0 disables automatic purging for
+that data type.
+
+      --api-keys-retention duration, $CODER_API_KEYS_RETENTION (default: 7d)
+          How long expired API keys are retained before being deleted. Keeping
+          expired keys allows the backend to return a more helpful error when a
+          user tries to use an expired key. Set to 0 to disable automatic
+          deletion of expired keys.
+
+      --audit-logs-retention duration, $CODER_AUDIT_LOGS_RETENTION (default: 0)
+          How long audit log entries are retained. Set to 0 to disable (keep
+          indefinitely). We advise keeping audit logs for at least a year, and
+          in accordance with your compliance requirements.
+
+      --connection-logs-retention duration, $CODER_CONNECTION_LOGS_RETENTION (default: 0)
+          How long connection log entries are retained. Set to 0 to disable
+          (keep indefinitely).
+
 TELEMETRY OPTIONS: 
 Telemetry is critical to our ability to improve Coder. We strip all personal
 information before sending data to our servers. Please only disable telemetry