SearchKit - Support form filters for relationships

[colemanw]

Overview

Makes it possible to filter related contacts by relationship fields.

Ref https://lab.civicrm.org/dev/core/-/issues/3468

Before

1. Create a search for a contact and a related contact
2. Create a search form
3. You can add filter fields for each contact, but not the relationship itself

After

[civibot]

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[kurund]

@colemanw

Looks good on the editor and now we can select relationship fields.

However, on search relationship fields are not displayed.

[colemanw]

@kurund - adding columns to a search display is a separate configuration and doesn't have to do with filters.
Oh, I see what you mean, the filter fields are missing in your second screenshot. I thought I fixed that but let me double-check.
If you applied this patch locally, did you clear caches?

[colemanw]

@kurund I just tried again and the filter fields are showing up for me. Try clearing caches.

[kurund]

@colemanw

Weird now it's working. Might be a caching issue or my mistake with applying the patch.

Good to merge.