Integrate GET endpoint for buckets and prefixes

[truemerrill]

@thecaffiend has finished the GET endpoint

curl -k https://api.cape-dev.org/capi-dev/rawobjstorage

This returns a JSON array of the following type

buckets: ObjectStore[] = [];

interface ObjectStore {
    objstore_name: string;
    prefixes: string[];
}

In the FileUpload component, when the component mounts, fetch the data from the GET endpoint and render the allowed buckets and prefixes to the end-user.