Regex/substring matching of collection names for quick lookup

**Is your feature request related to a problem? Please describe.**
In the new index preview, the long list of collections is hard to navigate, especially after already sorting by AD or KS value.

**Describe the solution you'd like**
A single text entry field for regex or substring matching against the list of collections, with only matching collections shown.

Locate the new index preview and the code that builds and sorts its collection list. Check how the existing AD and KS sorting is wired before deciding where the text entry belongs. Done means a regex or substring input is available and the preview shows only collections matching it.

Written by the indexing model from the issue text.