Environment banner not working if environment is not dev or prod

When using the new system property to display a environment banner in Solr UI, I cannot make it work.

First attempt with `-Dsolr.environment=unknown,color=red` gives the following error message on the UI: "Bad environment pattern: unknown,color=red".

Second attempt with just `-Dsolr.environment=unknown` gives no error but no banner appear nowhere.

Third attempt using "dev" or "prod" do work. Thus I'm guessing there is a list of allowed values?

I believe any value should be accepted as orgs can have various name for their environment, especially with ephemeral environment.

Or at least the documentation should mention the list of allowed values.