Fix cmip6 indicators bbox validation

[charparr]

This PR makes a small modification to the CMIP6 Indicators route such that it fetches the spatial bounds from rasdaman and constructs a bounding box to validate the lat-lon of the request.

This should enable locations to have both their CMIP6 data and CMIP6 indicators queried.

To test this PR, make sure you are pointing at datacubes and then try routes like this:

You should get data here:
http://localhost:5000/indicators/cmip6/point/50.5/-147

But not here:
http://localhost:5000/indicators/cmip6/point/49.5/-147

For the latter, the map isn't great but IMO that is OK for now. Also, the bounding box reported on this page is accurate due to the weirdness of the re-grid. However, any requests for latitude 90.1 or something will get caught by this block:

    validation = latlon_is_numeric_and_in_geodetic_range(lat, lon)
    if validation == 400:
        return render_template("400/bad_request.html"), 400

Closes #493

[cstephen]

Works great! Thanks for the quick fix, @charparr!