Custom notification banner is not working anymore

[bhavyarm]

Kibana version: 7.4.0 BC2

Elasticsearch version: 7.4.0 BC2

Server OS version: darwin_x86_64

Browser version: chrome latest/safari latest

Browser OS version: OS X

Original install method (e.g. download page, yum, from source, etc.): from staging

Describe the bug: Custom notification banners are not working anymore.

Steps to reproduce:

1. Go to advanced settings and look for "Custom banner notification"
2. Add some input text
3. Save it - refresh the browser - it doesn't display. Logout and login and it doesn't display

Expected behavior:

Custom notification banner should display

[elasticmachine]

Pinging @elastic/kibana-app

[bhavyarm]

Worked fine in 7.3.1

[lukeelmers]

i believe the global banners live inside ui/notify, a good chunk of which was cleaned up for 7.4 in #41663

not sure if this PR is actually what caused the regression, but it caught my attention

[kertal]

@lukeelmers yes, #41663 caused this regression

The following file is no longer imported
https://github.com/elastic/kibana/blob/master/src/legacy/ui/public/notify/notify.js

It contains

const config = chrome.getUiSettingsClient();

config.getUpdate$().subscribe(() => {
  applyConfig(config);
});

This applyConfig
https://github.com/elastic/kibana/blob/master/src/legacy/ui/public/notify/notify.js#L42
was responsible to apply the user-defined banner

Reenabling doesn't work, leads to a Cannot read property 'getUiSettingsClient' of undefinedException, the import of chrome here is undefined. This needs to be migrated, do you have an idea where to? Or how?

[elasticmachine]

Pinging @elastic/kibana-app-arch

[joshdover]

@kertal I have fixed this in #43610 where I move this code to the New Platform. That said, it's a bit more involved change (though not huge) that I'm not sure should be backported to a BC.

[kertal]

thx @joshdover, what alternatives do we have to backport, since as far as I can see, we can't just enable the old version of this banner?

[joshdover]

@kertal I'm going to see if I can't get a smaller focused fix to work. If not, I think we'll just backport that PR.

[joshdover]

Backport for 7.4 incoming: #45958