[Maps][Search Sessions] Pass down sessionId from embeddable to search calls

[lizozom]

We're aiming to release the MVP of Background Sessions (BGS) in 7.12.
The MVP supports saving BGS on Discover and Dashboard.

In order for a map on a dashboard to be saved with the session, the maps embeddable needs to take in the searchSessionId and pass it down to the search API.

searchSession.fetch({
...
sessionId,
});

If this is not done before 7.12, when users try to save a search session from a dashboard with a map, the map won't be stored and restored properly.

[elasticmachine]

Pinging @elastic/kibana-gis (Team:Geo)

[Dosant]

Some more details:

Search session are available under ff in master:

xpack.data_enhanced.search.sessions.enabled: true

Some prior art for reference:

• Pr that added this on a dashboard for some of other embeddable
  • Embeddable has to refetch when searchSessionId changes
  • If maps embeddable subscribes to timefilter.autorefresh$() it should be removed because since [Search] Search Sessions with relative time range  #84405 it is handled on a container dashboard level
• If maps code convert from relative to absolute time range without using a time filter helper, they should use nowProvider service: [Search] Search Sessions with relative time range  #84405

Please note:

• Functional tests for this feature. Should be useful for testing and adding maps specific tests.
• Unfortunately, we don't have example plugins or dev docs right now.
• This issue is only about making sure maps embeddable supports search sessions on a dashboard. Supporting search session in maps app is out of scope.