Cache bust import of .js files

[cb1kenobi]

The JSStore dynamically imports .js config files and the Layer class dynamically imports JOI schema .js files. The default import() function will internally cache modules, thus does not support reloading.

If we try to cache bust by inserting a timestamp in the file URI, Node will eventually crash if the module has been imported too many times. We need to wait and see if nodejs/node#49442 will solve the issue.