Filter modal fixes

[RobertJoonas]

Changes

• Display a loading spinner in the combobox when fetching suggestions for is and is_not filter operators.
• Extract lastLoadTimestamp from QueryContext into a new, separate context. This is currently causing unnecessary re-renders of any components depending on the queryContext. For instance, when keeping the combobox open, new options are fetched again every 30 seconds.
• Always consider contains and not_contains as freeChoice filter operators. Currently, the condition on which we consider a filter to be freeChoice is whether the filter key is one of ['screen', 'country', 'region', 'city']. This is wrong because these filters are simply the ones that do not support contains. It has nothing to do with being able to select a custom value to filter by.
• Fix does_not_contain not being a freeChoice operator in custom property filter modal.

Tests

• This PR does not require tests

Changelog

• This PR does not make a user-facing change

Documentation

• This change does not need a documentation update

Dark mode

• This PR does not change the UI

[github-actions]

Preview environment👷🏼‍♀️🏗️
PR-4553