Proposal/split dangling indices

[nhtruong]

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[codecov]

Codecov Report

Merging #475 (433b0ef) into main (fca8bd3) will increase coverage by 0.02%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main     #475      +/-   ##
==========================================
+ Coverage   70.92%   70.94%   +0.02%     
==========================================
  Files          81       84       +3     
  Lines        7732     7738       +6     
==========================================
+ Hits         5484     5490       +6     
  Misses       2248     2248              

Files Changed	Coverage Δ
...y/client/dangling_indices/delete_dangling_index.py	50.00% <50.00%> (ø)
...y/client/dangling_indices/import_dangling_index.py	50.00% <50.00%> (ø)
...y/client/dangling_indices/list_dangling_indices.py	75.00% <75.00%> (ø)
opensearchpy/client/dangling_indices/__init__.py	100.00% <100.00%> (ø)