feat: button to delete all files in index

[pvl]

Description

Implements a "delete all" button in index collection. Saw it as a requested feature in #317 and was something I had also needed.

Type of change

• [X ] New features (non-breaking change).
• [ ] Bug fix (non-breaking change).
• [ ] Breaking change (fix or feature that would cause existing functionality not to work as expected).

Checklist

• [X ] I have performed a self-review of my code.
• [ ] I have added thorough tests if it is a core feature.
• [X ] There is a reference to the original bug report and related work.
• [ ] I have commented on my code, particularly in hard-to-understand areas.
• [X] The feature is well documented.

[taprosoft]

Hi @pvl can you check the failed CI tests above :D

[pvl]

@taprosoft I've formatted the code with black now, sorry for missing that.