Minor AI impact utils improvements

What does this MR do and why?

This MR addresses some minor improvements for the AI impact utils:

• Updated namespace for translations
• Rename ai_impact/TABLE_METRICS constant to AI_IMPACT_TABLE_METRICS

MR acceptance checklist

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Screenshots or screen recordings

No visual changes

How to set up and validate locally

$ yarn jest analytics/dashboards

Related to #454637 (closed)

app/assets/javascripts/analytics/shared/constants.js

@@ -128,6 +128,10 @@ export const CONTRIBUTOR_METRICS = {
   COUNT: CONTRIBUTOR_COUNT_TYPE,
 };
 
+export const AI_METRICS = {
+  CODE_SUGGESTIONS_USAGE_RATE: 'code_suggestions_usage_rate',
+};
+
 export const METRIC_TOOLTIPS = {
   [DORA_METRICS.DEPLOYMENT_FREQUENCY]: {
     description: s__(
@@ -228,6 +232,14 @@ export const METRIC_TOOLTIPS = {
       anchor: 'view-the-number-of-merge-requests-in-a-date-range',
     }),
   },
+  [AI_METRICS.CODE_SUGGESTIONS_USAGE_RATE]: {
+    description: s__(
+      'AiImpactAnalytics|Monthly user engagement with AI Code Suggestions. Percentage ratio calculated as monthly unique Code Suggestions users / total monthly unique contributors.',
+    ),
+    groupLink: '',
+    projectLink: '',
+    docsLink: helpPagePath('user/analytics'),
+  },
 };
 
 // TODO: Remove this once the migration to METRIC_TOOLTIPS is complete