🌊 Move streams to platform (#211893)

This PR moves the `streams` and `streams_app` plugins into platform so
they can be used in other solutions in the future. This PR is not
actually making it available in other solutions yet since we are still
discussing the release plans.

## Inlined helpers

As discussed before, this PR inlines a couple simple helper methods for
query building, time zone normalization, a header portal helper and a
data plugin timefilter state react integration hook as there is no good
place for these outside of the observability solution.

## streams_app plugin

The streams_app plugin is not actually registering anything, instead it
simply exports a component that renders the app which needs to be
consumed by another plugin to turn it into a registered app - for now,
`observability_streams_wrapper` takes over this job.

## observability_streams_wrapper plugin

While 99% of the streams logic is moved into the
`platform/shared/streams_app`, two bits are left behind in
`observability_streams_wrapper`:
* The actual app registration
* Integration with the observability_shared `PageTemplate` component

Once we decide streams should be displayed outside of the observability
solution, it's probably not necessary anymore to decouple app definition
and registration like this because it will always be visible no matter
the solution. Once this is the case, the navigation registration can be
moved into the central `observability` plugin, like it's handled with
other apps like infra.

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

packages/kbn-optimizer/limits.yml

@@ -162,6 +162,7 @@ pageLoadAssetSize:
   stackConnectors: 67227
   streams: 16742
   streamsApp: 20537
+  streamsAppWrapper: 20537
   synthetics: 55971
   telemetry: 51957
   telemetryManagementSection: 38586