DOC: Fix missing periods and non capitalized summary beginnings (#27977)
- [ ] closes #27977 
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Fixed for the following functions
`pandas.io.formats.style.Styler.set_caption
pandas.plotting.table
pandas.plotting.register_matplotlib_converters
pandas.plotting.deregister_matplotlib_converters
pandas.arrays.IntervalArray.mid
pandas.Timedelta.ceil
pandas.Timedelta.floor
pandas.Period
pandas.Period.asfreq
pandas.Period.to_timestamp`

@WillAyd Cool, thanks for the quick review! And... *ping*, CI checks have passed. Thanks, @DanBenHa !