[EuiSearchBar/EuiSearchBarFilters] Allow exclusions in select value filter

[damian-polewski]

Problem Statement

EuiSearchBar/EuiSearchBarFilters components do not support allowing exclusion for FieldValueSelectionFilter.

Proposed Solution

Add allowExclusions prop to FieldValueSelectionFilterConfigType so it can be passed to EuiSelectable used in FieldValueSelectionFilter component.

Use Case

When working on elastic/kibana#229698 it was discovered that user cannot easily filter out the misconfigured repository and needs to either use the specific query in the search bar or needs to filter each repository individually to see all the snapshots.

Value / Impact

This improvement would allow users to filter out misconfigured repository easily.

Urgency

It's not a blocker but would certainly improve UX. Unfortunately there are no workarounds.