[2.x manual backport] BP for #7542, #7540, #7552, #7566, #7567

[ananzh]

Description

This is a backport PR for
Updating fetch functions to include local cluster 
#7542
Commit: 7287699

[discover-next][bug] add max height to dataset navigator and use memoization
#7540
Commit: 611f56b

Fix query assist after #7492, #7546, #7540
#7552
Commit: d68c589

[Discover next] Fixes dataset navigator menu styling & search error toast
#7566
Commit: 2b7dbe0

[Discover 2.0] Loading fix for databases
#7567
Commit: 8bafd8d

Issues Resolved

NA

Changelog

• skip

Check List

• All tests pass
  • yarn test:jest
  • yarn test:jest_integration
• New functionality includes testing.
• New functionality has been documented.
• Update CHANGELOG.md
• Commits are signed per the DCO using --signoff

[codecov]

Codecov Report

Attention: Patch coverage is 4.48718% with 149 lines in your changes missing coverage. Please review.

Project coverage is 63.73%. Comparing base (f2eaa6e) to head (63917ef).
Report is 1 commits behind head on 2.x.

Files	Patch %	Lines
.../public/ui/dataset_navigator/dataset_navigator.tsx	0.86%	114 Missing ⚠️
.../public/query/state_sync/connect_to_query_state.ts	16.66%	8 Missing and 2 partials ⚠️
...navigator/lib/utils/fetch_external_data_sources.ts	0.00%	8 Missing ⚠️
...ta/public/query/dataset_manager/dataset_manager.ts	12.50%	6 Missing and 1 partial ⚠️
.../dataset_navigator/lib/utils/fetch_data_sources.ts	0.00%	3 Missing ⚠️
...c/plugins/data/public/search/search_interceptor.ts	33.33%	2 Missing ⚠️
...ublic/query_assist/components/query_assist_bar.tsx	0.00%	2 Missing ⚠️
...ata/public/antlr/opensearch_sql/code_completion.ts	0.00%	1 Missing ⚠️
...query/state_sync/create_global_query_observable.ts	0.00%	1 Missing ⚠️
.../ui/dataset_navigator/create_dataset_navigator.tsx	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              2.x    #7574      +/-   ##
==========================================
- Coverage   63.75%   63.73%   -0.03%     
==========================================
  Files        3628     3628              
  Lines       79500    79525      +25     
  Branches    12593    12599       +6     
==========================================
  Hits        50682    50682              
- Misses      25753    25779      +26     
+ Partials     3065     3064       -1     

Flag	Coverage Δ
Linux_1	30.76% <1.31%> (-0.02%)	⬇️
Linux_2	55.70% <ø> (ø)
Linux_3	40.25% <3.28%> (-0.04%)	⬇️
Linux_4	31.69% <2.56%> (-0.02%)	⬇️
Windows_1	30.78% <1.31%> (-0.02%)	⬇️
Windows_2	55.65% <ø> (ø)
Windows_3	40.26% <3.28%> (?)
Windows_4	31.69% <2.56%> (-0.02%)	⬇️

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[ananzh]

Pls don't update branch. The missing one is a workspace PR which is not relevant to these bps.