Consolidate base url configuration on explorer UI plugins

[jackjia-ibm]

From review https://github.com/zowe/explorer-uss/pull/110#discussion_r544329917

apiml-static-registration.yaml.template routedServices:

• gatewayUrl: ui/v1 serviceRelativeUrl: /ui/v1/explorer-uss

@stevenhorsman stevenhorsman 2 days ago • Member I'm slightly concerned that we have this is 3 places now. If it's hardcoded here I'm not sure if it is needed in both manifest.yaml and package.json? Same situation for mvs and jes

[jackjia-ibm]

I found this is a little complicated to fix. We will also need a YAML parser to support parsing manifest in order to properly prepare FVT test environment. Right now we don't have a proper template, so are using the embedded environment variables as template format. I will come back to this later to solve this issue.

[AdarshdeepCheema]

@jackjia-ibm is this still an issue ?