Set window["_fs_csp"] via a config option passed to `init`

[patrick-fs]

Per this KB article: https://help.fullstory.com/hc/en-us/articles/360020622854-Can-I-use-Content-Security-Policy-CSP-with-FullStory-

There is a window["_fs_csp"] global variable that will load integrations in a separate script tag. Make this a config option passed into the init function.