feat(NODE-3446): deprecate mapReduce command

[ljhaywar]

Description

NODE-3446

What is changing?

The mapReduce command is being deprecated.

Is there new documentation needed for these changes?

No

What is the motivation for this change?

This command predates our aggregation framework and have functionality which is superseded by the aggregate command. We do not intend to add it into the stable API and instead should deprecate it to preserve a smaller and more consistent API going forward.

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: <type>(NODE-xxxx)<!>: <description>
• Changes are covered by tests
• New TODOs have a related JIRA ticket

[ljhaywar]

This is ready for review. I labeled this as "feat" as it seemed the best option. Should I label this as something else?

[dariakp]

LGTM, thanks! As far as the commit type - I think feat: makes the most sense, but I've also added it to our next tech chat agenda to see if we're onboard with codifying this

[ljhaywar]

Thanks, @dariakp!