Query by neighborhood

it would be nice to add an API endpoint something like:

```
GET registry.intermine.org/neighborhood/animals
```

returns the json for /instances, but filtered to:

```
flymine
humanmine
zebrafishmine
all other "animals" neighborhood intermines
```

that works for any/all neighborhoods configured.

Also nice to add this featuer to the UI!

Start by tracing the existing /instances endpoint and how configured neighborhoods are represented. Check how the UI discovers and displays registry instances. Done means a neighborhood-filtered endpoint works for every configured neighborhood and the corresponding UI feature is available.

Written by the indexing model from the issue text.