Docs for SERVER-34692: Move txnNumber in currentOp to subdocument

Description

Description:

Need to update currentOp

Engineering Ticket Description:

Currently txnNumber for inactive transactions is reported at the top level of each operation document, but it should be contained in a nested document like so:

{

transaction: {

parameters: {

txnNumber: ...

}

}

}

Scope of changes

Impact to Other Docs

MVP (Work and Date)

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