Improve Sumo Logic config screen

[kdhamric]

We want to improve the Sumo Logic tracing backend configuration screen in two ways:

AC1: Change the label from 'URL' to 'Sumo Logic API endpoint'

AC2: Change the 'Enter a URL' help text that appears in the textbox when empty from "Enter a URL" to "https://api.sumologic.com/api/"

AC3: Add a line directly below this text box that says: "This URL will be different based on your location. Use the Sumo Logic API endpoint as documented on 'Which endpoint should I use'."