Fixes CV-2037 - Add injectImmediately flag to main context snippets injection
This MR tries to solve the injection speed issue for main context snippets by adding the injectImmediately flag. We have a confluence page that explains the issue in more detail. We don't need to add the same flag to isolated context snippets as they are not time sensitive. Also updated the part of the README that was outdated. It now points to the npm package instead.