Add a dropbox to filter the Environment by Tag

Currently, in "Image Testing" > Select Image > left sidebar has a dropbox "Environment" or "Test plan" allowing to filter output by specific values.
It would be nice to have one more field such as "Environment Tag" for situations when several environments can be grouped under the same tag, so we don't have to select each environment from the long list.

Start in the Image Testing > Select Image view, focusing on the left sidebar's Environment and Test plan filters. Trace how those filters group and select environments, then add an Environment Tag filter that returns all environments sharing a tag; done means grouped environments can be filtered without selecting them individually.

Written by the indexing model from the issue text.