Add Empress to Qiita

[callaband]

I see so many papers using the Galaxy/LefSe taxonomy trees, it would be great to help Empress be even more accessible by adding it to Qiita. Any chance we could get Empire plots too?

[antgonza]

Update: during the last PR to update to qiime2-2021.2 I tried adding empress to the commands; however, this wasn't possible as it requires 3 inputs, 2 user defined via artifacts in an analysis; to be clear:

1. the tree: which currently can be selected from an artifact (SEPP) or one internally available (GG or WOL) // dropdown meny
2. the biom: which can be any biom
3. the pcoa: which can be any pcoa
   which means that the user needs to input 2 artifacts and we currently only support one.

Just opened qiita-spots/qiita#3087 - please join the discussion there!