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

docs/reference/api/general.md

@@ -463,6 +463,11 @@ curl -X GET http://coder-server:8080/api/v2/deployment/config \
       "disable_all": true
     },
     "redirect_to_access_url": true,
+    "retention": {
+      "api_keys": 0,
+      "audit_logs": 0,
+      "connection_logs": 0
+    },
     "scim_api_key": "string",
     "session_lifetime": {
       "default_duration": 0,