Description

Description:

This change introduces new builtin variables $$NOW and $$CLUSTER_TIME and we need the documentation.

Scope of changes

For this ticket, will just add to the

• 4.2 rel notes
• aggregation-variable page

We currently use $$NOW in the replaceRoot page, but a wholesale vetting of various pipeline examples to use these variables will be done as part on a different ticket.

Future work in July

Vet examples to use these variables.

Impact to Other Docs

MVP (Work and Date)

Resources (Scope or Design Docs, Invision, etc.)