BUG: Change root-proxies PUT url to not accept unsafe characters in a url

RM API uses "<n>" as an id for "none" root proxy.
In mod-kb-ebsco, when we make a PUT request, we provide the "id" of the root-proxy that needs to be selected like this:
PUT https://okapi.frontside.io/eholdings/root-proxies/<n>
Having "<n>" in the URL is unsafe and we should modify the code to serialize and de-serialize ""<n>", mapping it something like "None" in the URL but still passing "<n>" to RM API.

Acceptance Criteria:
After the change is made and deployed, ensure that we do not get a 500 response in Ebsco's devQA environment: http://fs00000000-fse-dev.s3-website-us-east-1.amazonaws.com/

requires backend and frontend change. May need a change to the root proxy None option displayed on the UI (settings > eholdings > root proxy)