DOC: create a table for period aliases
related to pr #53477
Updated documentation for [Time series / date functionality](https://pandas.pydata.org/docs/user_guide/timeseries.html#time-series-date-functionality)

Created a new table for `period aliases`. Added to the doc of `Period dtypes`reference to the table `period aliases` instead of [offset aliases](https://pandas.pydata.org/docs/user_guide/timeseries.html#timeseries-offset-aliases). Corrected docs for `to_period`. Pointed out that only frequencies from the table `period aliases` are valid for `to_period`. 
@MarcoGorelli,  could you please take a look at this pr? /preview Website preview of this PR available at: https://pandas.pydata.org/preview/53530/ > I just have a comment - you write "we will refer to these aliases as _period aliases_", but then in the `to_period` docstring you write "period strings". Perhaps that should say "period aliases" instead?
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Thank you, @MarcoGorelli for the comment. I corrected `to_period` docstring, as you suggested.
 Thanks @natmokval 