[Drilldowns] Dashboard url generator to preserve saved filters from destination dashboard

[Dosant]

Summary

Needed for #61219.

In drilldowns branch there is a bug with filters right now: When url to drilldown is generated and navigated to, fillers from URL always take precedence which makes sense for normal url flow, but doesn't make sense for navigation with drilldown.

This pr fetches destination dashboard in url generator and adds it's saved filters into resulting url.
Url generator doesn't do any error handling and just swallows errors if retrieving those filters wasn't successful.

Please refer to original discussion for more context: #63108 (comment)

So options:
Option 1: retrieve saved filters in Drilldowns code. Pass all filters to url generator
Option 2: retrieve saved filters inside url generator. merge them with incoming filters when generating url
Option 3: Url generator optionally adds additional flag in the url to also preserve saved filters: e.g. &savedFilters=merge. When dashboard is loaded it will use that flag to decided what to do with filters saved in dashboard.

This pr goes with Option 2 ⬆️
Initially I built Option 3: #64633

Checklist

Delete any items that are not applicable to this PR.

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for keyboard-only and screenreader accessibility
• This renders correctly on smaller devices using a responsive layout. (You can test this in your browser
• This was checked for cross-browser compatibility, including a check against IE11

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[majagrubic]

I know this is not a new change, but for my own understanding - why do we need to filter pinned filters here?

[Dosant]

url_generator accepts array of filters to apply and to make pinned state work in the url properly we have to split those into _a and _g :(

[majagrubic]

I tested this in Chrome 80 on Mac OS for the following scenarios (ie. existing functionality):

• loading saved query preserves filters
• add a new visualization to dashboard preserves filters
• sharing a dashboard via link preserves filters
• sharing a dashboard via embedding preserves filters
• sharing a dashboard via link > change original filters > filter is changed on the shared dashboard only
• sharing a dashboard via embedding > change original filters > filter is changed

I then followed @Dosant 's suggestion and added the following snippet at the end of start function in the dashboard plugin:

plugins.share?.urlGenerators
      .getUrlGenerator(DASHBOARD_APP_URL_GENERATOR)
      .createUrl({ dashboardId: 'some-dashbord', filters: [] })
      .then(url => {
        alert(url);
      });

This threw an error as expected.

Codewise, a lot cleaner than adding this in the URL. 🚢

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 5b8d489

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