Add search to label tree page

[dlangenk]

On the label tree page https://biigle.de/label-trees/ there is no search for a label. If you want to rename or delete a label it might be hard to find in a bigger tree. The functionality is already implemented with the Label Parent box. However having a dedicated search would be appreciated if this is not too complex to achieve.

This was also requested here: https://github.com/orgs/biigle/discussions/971