DOCS Clone for 3.4.16 and 3.6.6: Add syncSourceHost field to replSetGetStatus output

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Original Description

Description:

We're deprecating the old "syncingTo" field in 4.0. We should remove references to this field in our docs, and replace them with references to "syncSourceHost"

Scope of changes:

• replSetGetStatus
  • add new field
  • deprecate old field
  • update sample output
  • update missing output fields
    • syncSourceId (DOCS-11699) <<-- also backported
    • top level syncingTo , "syncSourceHost" : "", "syncSourceId" : -1

Impact to other docs outside of this product:

None

MVP:

Resources:

Engineering Ticket Description:

The 'syncingTo' field in replSetGetStatus output is ambiguously named. To make it clear what direction the replication is going in, we will add a new field "syncSourceHost" with the same data as the existing "syncingTo". In a later version we will remove "syncingTo".
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Description

Need to backport commit from master to 3.4.16 and 3.6.6 – but must double check which parts of the commit needs to be backported.

• The stable checkpoint time shouldn't be backported.
• versionchanged

Scope of changes (files that need work and how much)

Impact to other docs outside of this product

MVP (work and date?)

Resources (e.g. Scope Docs, Invision)