Stabilize Discover telemetry context assertions in FTR (elastic#263224)

The Discover context-awareness functional test was intermittently
failing on CI when `performance_metric` telemetry had not arrived within
the test’s fetch window.

## Changes Made

- Increased `withTimeoutMs` from `500` to `1500` for the two affected
`performance_metric` event fetches in
`src/platform/test/functional/apps/discover/context_awareness/_telemetry.ts`
- Kept the original assertion flow for those checks without adding retry
wrappers or new guard assertions

This keeps the fix narrowly focused on giving telemetry more time to
arrive in slower CI runs while preserving the original test structure.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: davismcphee <25592674+davismcphee@users.noreply.github.com>

Author: Copilot

src/platform/test/functional/apps/discover/context_awareness/_telemetry.ts

@@ -32,6 +32,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
   const kibanaServer = getService('kibanaServer');
   const dashboardAddPanel = getService('dashboardAddPanel');
   const toasts = getService('toasts');
+  const performanceMetricTimeoutMs = 1500;
 
   describe('telemetry', () => {
     describe('context', () => {
@@ -61,7 +62,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
 
         const events = await ebtUIHelper.getEvents(Number.MAX_SAFE_INTEGER, {
           eventTypes: ['performance_metric'],
-          withTimeoutMs: 500,
+          withTimeoutMs: performanceMetricTimeoutMs,
         });
 
         expect(events[events.length - 1].context.discoverProfiles).to.eql([
@@ -81,7 +82,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
 
         const events = await ebtUIHelper.getEvents(Number.MAX_SAFE_INTEGER, {
           eventTypes: ['performance_metric'],
-          withTimeoutMs: 500,
+          withTimeoutMs: performanceMetricTimeoutMs,
         });
 
         expect(events[events.length - 1].context.discoverProfiles).to.eql([