ENH: Filtering Tutorial to include SampleData

**Improvement Description**
Add description on how to filter `SampleData` in [Filtering Data Tutorial](https://docs.qiime2.org/2021.4/tutorials/filtering/).

**Current Behavior**
Examples cover how to filter `FeatureTable` but not `SampleData`.

**Proposed Behavior**
Examples on filtering `SampleData` with `qiime demux filter-samples`
