Add background SCM sync

On page save, it should queue an SCM sync.

Things to answer:

Should changes be saved to disk until about to sync SCM (so queued tasks would: flush to disc, sync to SCM and repeat)
How would served pages be loaded - should there be an in-memory cache of 'latest' version?
Should this functionality be enable-able as a feature?

Edited Aug 04, 2021 by Matt