Similar to the transactions diagnostics project, we want to maintain certain metrics in the serverStatus section. The TransactionsSSS::generateSection method returns a BSON object that goes into the transactions section of the serverStatus output.

This ticket can be split into multiple commits if needed. We will want to output:

• the total number of prepared transactions

• the total number of committed prepared transactions
• the total number of aborted prepared transactions

We will need to add these counters to ServerTransactionMetrics and the transactions_stats.idl class, so that we can serialize these counters to the serverStatus output object in the TransactionsSSS::generateSection method.

We will also update the TransactionMetricsObserver to increment/decrement the stats when appropriate.