Allow altering the built snippet

Problem/Motivation

In order to selectively enable the Hotjar script based on if the user accepted cookies or not, we want to be able to wrap the Hotjar snippet in a function. Currently the Hotjar module has no way of altering the snippet that is output.

Proposed resolution

An alter hook on the snippet script in SnippetBuilder::buildSnippet would allow the script to be wrapped. It does mean that the alter is never called when the script is included as a Drupal attachment. The API function should document this exception.

A patch is attached that adds and documents the hook.

API changes

A new hook is added, hook_hotjar_snippet_alter(), which receives the generated Hotjar snippet script by reference.

Release notes snippet

Added a hook for altering a built Hotjar snippet.