Apply category notification preferences to existing users

[dax (Daniela)]

There is a guide to read for that:

(Obsolete) Set category tracking level defaults historically

Following the release of Discourse v2.4.0.beta7 (or if you have this commit), admins now have the option to set the category tracking levels of all existing users when setting the default category tracking levels in their site settings: Add a category to one of the following site settings, then select the green checkbox button. [10%20PM] A modal window will pop up with the following options: [10%20PM] The old way using the console