SNOW-1791556: Use docstrings folder for Index methods and properties (#2581)

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   Fixes SNOW-1791556

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3. Please describe how your code solves the related issue.

Use docstrings folder for Index methods and properties. Docstrings for
DatetimeIndex and TimedeltaIndex will be treated similarly in follow-up
PRs.

Author: sfc-gh-helmeleegy

src/snowflake/snowpark/modin/plugin/docstrings/__init__.py

@@ -11,6 +11,7 @@
     DataFrameGroupBy,
     SeriesGroupBy,
 )
+from snowflake.snowpark.modin.plugin.docstrings.index import Index
 from snowflake.snowpark.modin.plugin.docstrings.io import *  # noqa: F401,F403
 from snowflake.snowpark.modin.plugin.docstrings.resample import Resampler
 from snowflake.snowpark.modin.plugin.docstrings.series import Series
@@ -31,4 +32,5 @@
     "Series",
     "SeriesGroupBy",
     "StringMethods",
+    "Index",
 ]