ENH: Add read_logfmt()
- [x] closes #34501 
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Doesn't pass CI yet becasue conda-forge does not have `logfmt` package.

Waiting for it to be approved: https://github.com/conda-forge/staged-recipes/pull/11779 > can u open an issue for discussion about this first

Did not know it was required, [contributing guide](https://pandas.pydata.org/docs/development/contributing.html) asks to search for issue, but "Bug reports and enhancement requests" section does not discuss enhancement requests. Here is an issue: https://github.com/pandas-dev/pandas/issues/34501