Provide actionable error message in case uploadEnabled is undefined

Author: brizental

glean/src/core/context.ts

@@ -79,6 +79,8 @@ export class Context {
         LOG_TAG,
         [
           "Attempted to access Context.uploadEnabled before it was set. This may cause unexpected behaviour.",
+          "Please double check if a boolean value was passed to `Glean.setUploadEnabled`",
+          "or to the `uploadEnabled` value on `Glean.initialize`."
         ],
         LoggingLevel.Error
       );