PERF: GH28635 Add ASV benchmark for resample after groupby
- [x] closes #28635 (Replace xxxx with the GitHub issue number)
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- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
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- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

> What is the runtime of the benchmark? We aim for something like 20ms in general

The code as I had first submitted it took 100ms per tested function for one run on my machine, I reduced the size of the dataset so that it is below 20ms now on my machine [1]. Of course my machine is not necessarily representative... If this is not the right aproach, anything I should be doing differently?


```
asv run -e -E existing -b groupby.Resample --durations

[25.00%] ··· Running (groupby.Resample.time_resample--)..
[75.00%] ··· groupby.Resample.time_resample                                       16.2±0.4ms
[100.00%] ··· groupby.Resample.time_resample_multiindex                           16.9±0.5ms
[100.00%] ·· =========================================== ================
                              benchmark                   total duration 
             ------------------------------------------- ----------------
              groupby.Resample.time_resample_multiindex       508ms      
                    groupby.Resample.time_resample            508ms      
                                total                         1.02s      
             =========================================== ================

```
 Great, thx thx @krasch 