Convert compute metadata files from JSON to JS

[brollb]

This would add support for dynamism in the metadata files and would be a nice enhancement. The specific motivation is given below.

Adding support for #1999 requires that we are able to resolve usernames to tokens and is required by both the compute and storage clients. Ideally, we would use the same approach for both storage and compute clients. The storage clients are run in the browser and in the compute environment so values like SciServer tokens must be resolved in the browser (authenticated requests to deepforge are not necessarily possible in the compute environment).