feat: add drop_index

[westonpace]

Helpful for when an index is created by mistake or no longer needed.

[LuQQiu]

is column required? or solely name is enough?

[westonpace]

Good point. I didn't realize index names were unique but after some testing it appears this is the case. So the name should be all we need 🎉

I'll fix the PR.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 97.87234% with 2 lines in your changes missing coverage. Please review.

Project coverage is 78.46%. Comparing base (4d77d7b) to head (0ef9b92).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
rust/lance/src/index.rs	97.87%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3382      +/-   ##
==========================================
- Coverage   78.47%   78.46%   -0.01%     
==========================================
  Files         250      250              
  Lines       90243    90433     +190     
  Branches    90243    90433     +190     
==========================================
+ Hits        70817    70960     +143     
- Misses      16521    16557      +36     
- Partials     2905     2916      +11     

Flag	Coverage Δ
unittests	78.46% <97.87%> (-0.01%)	⬇️

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[wjones127]

Nice work!