Instant Search: Allow multiple select on Date filter

### Impacted plugin

Search

### What

Add a setting for whether or not the date filter should be subtractive for other date filter results

### How

Allowing the Date (Year and Month) filter options to not exclude other dates would be helpful if you've selected your filters and want to see posts from both 2022 and 2023, for example.

This is helpful to narrow down the search without excluding "everything" else regarding dates.

Backend setting:

Frontend result:

Start by tracing the Search plugin's backend date-filter setting and the corresponding frontend result shown in the issue. Confirm how Year and Month filters currently exclude one another, then verify that the setting allows multiple selected dates such as 2022 and 2023 without excluding other date results.

Written by the indexing model from the issue text.