Add: Documentation of new option to disable cf_promises_validated

Ref: https://dev.cfengine.com/issues/6688
Don't merge without: https://github.com/cfengine/masterfiles/pull/340
Merge pull request #948 from nickanderson/option_cf_promises_validated

Add: Documentation of new option to disable cf_promises_validated
adjust timelines
Change: Fix missing link reference
Merge pull request #951 from nickanderson/fix/docs

Change: Fix missing link reference