[Drilldowns] URL drilldown better URL preview

[Dosant]

Part of #55324

There is a confusing UX edge case with URL preview in initial URL drilldown implementation #69409

When drilldown is created, editor component doesn't know much about underlying data shape.
In preview it just relies on typescript shape of trigger's context.

Edge cases that we don't cover:

1. Array of points: ({{event.points}}). The number of points in the array in preview could be different from runtime
2. Different types. For example: {{event.from}} could be a date or a number. In preview we assume it is date. In runtime it could be a number
3. Impossible to test against conditions.

In this issue I explained this edge cases in details: #76226

We should explore if we could solve this by:

1. Providing samples of trigger context to drilldown editor
2. Relying on more detailed triggers instead of generic value_click and range_select
3. Now mock values are hardcoded, but we could allow users to manually edit those to test out different scenarios. This would be especially useful when we create a drilldown template (no access to real data on this point). @Dosant: to link an issue

[elasticmachine]

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

[streamich]

Closing this as we removed preview feature, as {{event.*}} scoped variables are too dynamic to construct a correct preivew.