Fix highlight config so it doesn't require a refresh to apply

[lukasolson]

Prior to this PR, when you would go into the advanced settings and change the doc_table:highlight to false (or true), it would require refreshing the page before it would be applied. This was confusing.

This PR fixes this behavior such that the config is checked each time we go to apply highlighting instead of only when the page loads, and adds a test surrounding this behavior.

Fixes #7796.

[Bargs]

This looks pretty good. I did find one edge case. If you add a saved search from a pre 5.3 installation to a dashboard you'll still get highlighting even if doc_table:highlight is false because the highlighting config is stored with the saved object. It works on discover because we always set highlightAll to true which causes the saved object highlighting to get ignored. I think if we do the same on Dashboard we should be good.

[lukasolson]

Good catch, @Bargs.

[lukasolson]

@Bargs Could you take another look? Thanks!

[Bargs]

LGTM!

[lukasolson]

jenkins, test this

[lukasolson]

Backported to 5.3 in 3b34f16.
Backported to 5.x (5.4) in d54757b.

[bhavyarm]

@lukasolson I had discover and advanced settings open in two separate tabs(chrome latest). Then I tried setting the value of doc_table:highlight and looked at the results in discover. The settings didn't get applied till I refreshed the page. Is this expected.

cc @Bargs this works fine otherwise. What we saw together in zoom - I couldn't reproduce it in local. Thanks!