Add the ability to untrack custom fields in page specific options

[bencroker]

This idea needs to be further explored, but the general idea is to add the ability to specify that custom fields should be ignored when elements are tracked in parts of the page via page specific options. This could be especially useful if outputting a navigation menu or list of entry titles and URLs. The benefit of doing this is that Blitz needs to refresh fewer pages when only custom fields are updated in the entries.

[bencroker]

As of version 4.4.0, Blitz automatically tracks which custom fields are output per element per page without requiring manual intervention, as well as which attributes and custom fields are changed on each element save, greatly reducing the number of cached pages that must be invalidated when content changes