Fix SS03 Issues in Docstrings
Running the following:
```scripts/validate_docstrings.py --errors=SS03``` 
returns the following instances of cases where the Summary doesn't end with a period. 
SS03 is one of the pending docstring-related errors as mentioned in #27977



- [ ] pandas.tseries.frequencies.to_offset: Summary does not end with a period
- [ ] pandas.Int64Index: Summary does not end with a period
- [ ] pandas.UInt64Index: Summary does not end with a period
- [ ] pandas.Float64Index: Summary does not end with a period
- [ ] pandas.IntervalIndex.left: Summary does not end with a period
- [ ] pandas.IntervalIndex.right: Summary does not end with a period
- [ ] pandas.IntervalIndex.mid: Summary does not end with a period
- [ ] pandas.IntervalIndex.closed: Summary does not end with a period
- [ ] pandas.IntervalIndex.length: Summary does not end with a period
- [ ] pandas.io.stata.StataReader.data: Summary does not end with a period
- [ ] pandas.plotting.plot_params: Summary does not end with a period
- [ ] pandas.io.formats.style.Styler.loader: Summary does not end with a period
- [ ] pandas.Timestamp.combine: Summary does not end with a period
- [ ] pandas.Timestamp.fromordinal: Summary does not end with a period
- [ ] pandas.Timestamp.isoweekday: Summary does not end with a period
- [ ] pandas.Timestamp.weekday: Summary does not end with a period
- [ ] pandas.Period.strftime: Summary does not end with a period
- [ ] pandas.Interval.closed: Summary does not end with a period
- [ ] pandas.Interval.left: Summary does not end with a period
- [ ] pandas.Interval.length: Summary does not end with a period
- [ ] pandas.Interval.mid: Summary does not end with a period
- [ ] pandas.Interval.right: Summary does not end with a period

The way to go about resolving this issue with such a large number of files has been nicely setup by @datapythonista in #27977 itself. Quoting from the issue:

_**> VERY IMPORTANT
The main challenge will be not repeating the same work as other sprinters, which is very frustrating, and happened massively at every sprint. My recommendation is BEFORE doing any work, to create an issue for the error code you plan to work on (check that it hasn't already been created). In the error write the list of errors that validate_docstrings.py returns. Then in a comment, take 10 of them, and write that you're going to fix them. Other people can work on a different 10. When opening a PR, reference the issue.**_


[UPDATE 1] 
List has been updated after @datapythonista's recommendation to remove the ones starting with ```pandas.tseries.offsets``` .
