Allow access and dual access together

[trevorgerhardt]

Support creating both types of accessibility analysis in a single regional analysis in the future.

These changes accomplish this by:

1. Changing dual access filenames from {id}_{destinationsId}_p{percentile}.access to {id}_{destinationsId}_p{percentile}.dual.access so the names do not clash with regular accessibility results (a similar change is applied to the derived single threshold grid files).
2. Adding a dualAccessValues parameter to RegionalWorkResult so that the accessibilityValues parameter is not overwritten with dual access values.

Notably, this does not require any UI changes at this time. The staging UI currently only allows creating one type at a time. When viewing results, getRegionalResults retrieves a single type depending on how it was created. Once the UI allows it in the future, we can add a query parameter to getRegionalResults to select between the different results.