Add performance events for test-service-load client election

[kian-thompson]

We are seeing weird gaps in summarizer in test-service-load runs. This PR adds optional performance events (only enabled in test-service-load) to track adding, removing, and electing clients.

[msfluid-bot]

⯅ @fluid-example/bundle-size-tests: +4 KB

Metric Name	Baseline Size	Compare Size	Size Diff
aqueduct.js	452.91 KB	453.91 KB	⯅ +1023 Bytes
azureClient.js	550.15 KB	551.15 KB	⯅ +1023 Bytes
connectionState.js	680 Bytes	680 Bytes	■ No change
containerRuntime.js	256.75 KB	257.75 KB	⯅ +1023 Bytes
fluidFramework.js	359.58 KB	359.58 KB	■ No change
loader.js	132.91 KB	132.91 KB	■ No change
map.js	41.45 KB	41.45 KB	■ No change
matrix.js	143.67 KB	143.67 KB	■ No change
odspClient.js	518.69 KB	519.69 KB	⯅ +1023 Bytes
odspDriver.js	97.29 KB	97.29 KB	■ No change
odspPrefetchSnapshot.js	42.15 KB	42.15 KB	■ No change
sharedString.js	160.19 KB	160.19 KB	■ No change
sharedTree.js	359.58 KB	359.58 KB	■ No change
Total Size	3.19 MB	3.2 MB	⯅ +4 KB

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Baseline commit: d42d16d

Generated by 🚫 dangerJS against 3f30208

[vladsud]

I think every time we get here, we should log an event (i.e. not sample / hide it behind feature gate).
That's not many events - we issue a ton events before we get here (overall).

Analyzing code, I think the only reason "ElectedClientNotSummarizing" is not firing is because this.clientElection.electionSequenceNumber keep advancing, and that means tryElectingClient() is called (FYI - the only place it path be called in case of that stress test failure looks like from resetElectedClient()).

Given that we could run into these issues in prod as well, I'd rather prep us for more actionable future even if we do not enable new feature gate.

[vladsud]

Tracing the code, this function should never be called with this._electedClient === client, so maybe we should replace it with assert? Maybe incrementElectedClient() / resetElectedClient() can result in calling with existing client (not sure), but they are not called anywhere.

The more I think about it, the more I want to see the following telemetry in prod (properties on event that fires every time this function is called):

• reason (passed from caller) for summarizer election (i.e. summarizer client removed to quorum, summarizer parent removed from quorum, new summarizer client added).
• old value of this._electedClient?.clientId
• new value (client?.clientId).
• if new client is a summarizer client or not.
• other properties that you are adding.