[bsearch] repetitive uiSettings access on each search

[spalger]

Kibana version: master
Elasticsearch version: master
Server OS version: CI

Description of the problem including expected versus actual behavior: When bsearch receives multiple search requests for strategy ese_search I'm noticing that every query makes its own call to uiSettingsClient.get(UI_SETTINGS.SEARCH_INCLUDE_FROZEN), which results in many unnecessary requests being fired of to ES at the same time:

Steps to reproduce:

1. Run Kibana with APM enabled
2. Load up a dashboard with multiple visualizations
3. Checkout the APM data to find POST /internal/bsearch transactions, then flip through them and see that they send many requests to ES for the same document at the same time.

[spalger]

Location of the mentioned call:

kibana/src/plugins/data/server/search/strategies/ese_search/request_utils.ts

Line 25 in 328c36d

const includeFrozen = await uiSettingsClient.get(UI_SETTINGS.SEARCH_INCLUDE_FROZEN);

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServices)