Investigate changes in SERVER-41499: Track number of elections called for each reason in serverStatus

Description

SERVER ticket description: We want to track the number of elections called for each of the following reasons: Step Up, Priority Takeover, Catchup Takeover, Election Timeout, and Freeze Timeout. Specifically, we only want to track if an actual election is called (and not a dry run), which will involve incrementing the respective counter once the real election is started.
Change Description: Added 'electionMetrics' section to serverStatus.

Scope of changes

Impact to Other Docs

MVP (Work and Date)

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