ENH: Make metadata from read_spss available 
#### Is your feature request related to a problem?
I would like to have the [metadata that pyreadstats provides](https://ofajardo.github.io/pyreadstat_documentation/_build/html/index.html) available when reading files from SPSS. 

This would be really helpful because it would provide an easy way to have variable labels (descriptions), value labels, and other important metadata available to format results/reports (by replacing the variable names manually with `.replace` function). 

Those kinds of metadata are widely used in social sciences because it makes understanding results really easy. For example, SPSS changes the variable names to the variable labels in the output of analyses. Users could manually do this if the metadata was available.

#### Describe the solution you'd like
The metadata read by pyreadstats could be stored in the df's `_metadata` attribute and that would make it readily available

#### API breaking implications
I don't think there would be any implications if it's stored in the `_metadata` attribute because it was developed for this kind of use-case. I'm I right?

#### Describe alternatives you've considered
I could use the pyreadstats directly without using the `df.read_spss`. I can't think of any other options.

#### Additional context
This is related to issues [#11179](https://github.com/pandas-dev/pandas/issues/11179) and [#39](https://github.com/pandas-dev/pandas/issues/39).