DOC: Enforce Numpy Docstring Validation for pandas.DatetimeIndex.freqstr (#58309)

* DOC: add SA01 to pandas.DatetimeIndex.freqstr

* DOC: remove pandas.DatetimeIndex.freqstr

* DOC: removed pandas.PeriodIndex.freqstr

Author: tuhinsharma121

ci/code_checks.sh

@@ -98,7 +98,6 @@ if [[ -z "$CHECK" || "$CHECK" == "docstrings" ]]; then
         -i "pandas.DataFrame.swaplevel SA01" \
         -i "pandas.DataFrame.to_markdown SA01" \
         -i "pandas.DataFrame.var PR01,RT03,SA01" \
-        -i "pandas.DatetimeIndex.freqstr SA01" \
         -i "pandas.DatetimeIndex.indexer_at_time PR01,RT03" \
         -i "pandas.DatetimeIndex.snap PR01,RT03" \
         -i "pandas.DatetimeIndex.std PR01,RT03" \
@@ -203,7 +202,6 @@ if [[ -z "$CHECK" || "$CHECK" == "docstrings" ]]; then
         -i "pandas.PeriodIndex.dayofyear SA01" \
         -i "pandas.PeriodIndex.days_in_month SA01" \
         -i "pandas.PeriodIndex.daysinmonth SA01" \
-        -i "pandas.PeriodIndex.freqstr SA01" \
         -i "pandas.PeriodIndex.from_fields PR07,SA01" \
         -i "pandas.PeriodIndex.from_ordinals SA01" \
         -i "pandas.PeriodIndex.hour SA01" \

pandas/core/arrays/datetimelike.py

@@ -875,6 +875,11 @@ def freqstr(self) -> str | None:
         """
         Return the frequency object as a string if it's set, otherwise None.
 
+        See Also
+        --------
+        DatetimeIndex.inferred_freq : Returns a string representing a frequency
+            generated by infer_freq.
+
         Examples
         --------
         For DatetimeIndex: