Docs for SERVER-38984: Attach IDs to users

Description

Description:

User document schema now has an additional field 'userId' which contains a unique UUIDv4 value per user.

Engineering Ticket Description:

It would be useful if user documents could store an identifier unique to the user.

Scope of changes

• source/core/security-users.txt
• source/reference/command/createUser.txt
• source/reference/command/updateUser.txt
• source/reference/command/usersInfo.txt
• source/reference/method/db.createUser.txt
• source/reference/method/db.updateUser.txt
• source/reference/system-users-collection.txt

Impact to Other Docs

MVP (Work and Date)

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