Recognize other out-of-the-box metrics dashboards

Instead of recognizing only the common_metrics dashboard, allow any
dashboard defined under config/prometheus folder.

app/assets/javascripts/monitoring/constants.js

@@ -208,6 +208,14 @@ export const annotationsSymbolIcon = 'path://m5 229 5 8h-10z';
  */
 export const DEFAULT_DASHBOARD_PATH = 'config/prometheus/common_metrics.yml';
 
+/**
+ * GitLab provide metrics dashboards that are available to a user once
+ * the Prometheus managed app has been installed, without any extra setup
+ * required. These "out of the box" dashboards are defined under the
+ * `config/prometheus` path.
+ */
+export const OUT_OF_THE_BOX_DASHBOARDS_PATH_PREFIX = 'config/prometheus/';
+
 export const OPERATORS = {
   greaterThan: '>',
   equalTo: '==',

app/assets/javascripts/monitoring/stores/utils.js

@@ -6,7 +6,7 @@ import { mergeURLVariables, parseTemplatingVariables } from './variable_mapping'
 import { DATETIME_RANGE_TYPES } from '~/lib/utils/constants';
 import { timeRangeToParams, getRangeType } from '~/lib/utils/datetime_range';
 import { isSafeURL, mergeUrlParams } from '~/lib/utils/url_utility';
-import { NOT_IN_DB_PREFIX, linkTypes, DEFAULT_DASHBOARD_PATH } from '../constants';
+import { NOT_IN_DB_PREFIX, linkTypes, OUT_OF_THE_BOX_DASHBOARDS_PATH_PREFIX } from '../constants';
 
 export const gqClient = createGqClient(
   {},
@@ -479,7 +479,7 @@ export const normalizeCustomDashboardPath = (dashboard, dashboardPrefix = '') =>
     dashboardPath = '';
   } else if (
     currDashboard.startsWith(dashboardPrefix) ||
-    currDashboard.startsWith(DEFAULT_DASHBOARD_PATH)
+    currDashboard.startsWith(OUT_OF_THE_BOX_DASHBOARDS_PATH_PREFIX)
   ) {
     dashboardPath = currDashboard;
   }

spec/frontend/monitoring/store/utils_spec.js

@@ -877,6 +877,8 @@ describe('normalizeCustomDashboardPath', () => {
     ${['.gitlab/dashboards/links.yml', '.gitlab/dashboards']}           | ${'.gitlab/dashboards/links.yml'}
     ${['.gitlab/dashboards/dir1/links.yml', '.gitlab/dashboards']}      | ${'.gitlab/dashboards/dir1/links.yml'}
     ${['.gitlab/dashboards/dir1/dir2/links.yml', '.gitlab/dashboards']} | ${'.gitlab/dashboards/dir1/dir2/links.yml'}
+    ${['config/prometheus/pod_metrics.yml', '.gitlab/dashboards']}      | ${'config/prometheus/pod_metrics.yml'}
+    ${['config/prometheus/pod_metrics.yml']}                            | ${'config/prometheus/pod_metrics.yml'}
   `(`normalizeCustomDashboardPath returns $expected for $input`, ({ input, expected }) => {
     expect(normalizeCustomDashboardPath(...input)).toEqual(expected);
   });