[feature request] FilterInputLabel: show how many alerts are discarded for a negative query

[dmke]

When using negative queries like instance!=server1 or instance!~^server\d\d$, Karma currently shows the number of matching alerts:

https://demo.karma-dashboard.io/?q=%40cluster%3DHA&q=%40receiver%3Dby-cluster-service&q=instance%21~%5Eserver%5Cd%5B234%5D%5Cd%3F%24

It would be nice however, if the label could show the difference to the total, i.e. the number of alert which were filtered out by this query, something akin to this:

This becomes useful when there are many alerts filtered:

[github-actions]

This issue has been automatically marked as stale because it has not had
recent activity. It will be closed if no further activity occurs. Thank you
for your contributions.