🌊 Reset materialized time range on app load (#222219)

The `useTimefilter` hook that's used throughout the streams UI is
retaining the last resolution of date math to absolute time ranges. This
is helpful to keep the time range stable when switching pages within the
app or making changes on a single page (like testing different grok
patterns) without completely using the current context.

However, it's confusing to move from another app like Discover to the
Streams app because the last resolution might be outdated quite a bit:
* Start in streams with a time range of last 15 mins
* Go to Discover and trigger new searches for 5 mins without changing
the time range - Discover updates the time range on each request (always
resolving "last 15mins")
* Go back to Streams - "last 15mins" still resolves to the last state
from 5 mins ago - if the user has seen a doc in discover, it probably
won't show in the streams UI without the user hitting refresh

This PR improves this user flow by resetting the resolved time range
when loading the streams app - it's kept stable while navigating around
within streams to stay consistent in there but updates once moving away
from the streams UI.

This is not fully solving the issue but it tries to balance the
advantages of the different approaches without too much effort in the
near term. This change does not affect the behavior of Discover or other
apps at all.

---------

Co-authored-by: Thom Heymann <190132+thomheymann@users.noreply.github.com>

src/platform/plugins/shared/data/public/query/timefilter/timefilter.ts

@@ -116,6 +116,10 @@ export class Timefilter {
    */
   public getAutoRefreshFetch$ = () => this.autoRefreshLoop.loop$;
 
+  public triggerFetch = () => {
+    this.fetch$.next();
+  };
+
   public getFetch$ = () => {
     return this.fetch$.asObservable();
   };

src/platform/plugins/shared/data/public/query/timefilter/timefilter_service.mock.ts

@@ -37,6 +37,7 @@ const createSetupContractMock = () => {
     enableTimeRangeSelector: jest.fn(),
     getBounds: jest.fn(),
     calculateBounds: jest.fn(),
+    triggerFetch: jest.fn(),
     createFilter: jest.fn(),
     createRelativeFilter: jest.fn(),
     getRefreshIntervalDefaults: jest.fn(),

x-pack/platform/plugins/shared/streams_app/public/plugin.tsx

@@ -71,6 +71,12 @@ export class StreamsAppPlugin
             PageTemplate,
             telemetryClient: this.telemetry.getClient(),
           };
+
+          // Trigger fetch to ensure the time filter has an up-to-date time range when the app mounts.
+          // This is done to ensure that dynamic time ranges (like "Last 15 minutes") are applied like they
+          // would be in discover or dashboards.
+          pluginsStart.data.query.timefilter.timefilter.triggerFetch();
+
           return (
             <StreamsApplication
               coreStart={coreStart}