Set _hipscat_index as pandas index, where possible.

[delucchi-cmu]

Closes #67

If the field _hipscat_index is present and NOT the index, set the pandas index in both the meta and incoming dataframes.

[github-actions]

Before [cb30209]	After [9f8c913]	Ratio	Benchmark (Parameter)
failed	failed	n/a	benchmarks.time_box_filter_on_partition
failed	93.5±2ms	n/a	benchmarks.time_kdtree_crossmatch
25.9±0.3ms	27.3±0.7ms	1.05	benchmarks.time_polygon_search
1.72±0.01s	1.75±0.01s	1.02	benchmarks.time_create_midsize_catalog
11.5±0s	11.6±0.07s	1.01	benchmarks.time_create_large_catalog

Click here to view all benchmarks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.87%. Comparing base (cb30209) to head (e62f365).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #415   +/-   ##
=======================================
  Coverage   97.86%   97.87%           
=======================================
  Files          44       44           
  Lines        1547     1553    +6     
=======================================
+ Hits         1514     1520    +6     
  Misses         33       33           

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