Isolate summarizer client election logic

[arinwt]

As requested by #6335 to split into separate PRs.

This change isolates the existing elected summarizer logic into its own class outside of SummaryManager. The new class is SummarizerClientElection, which depends on an OrderedClientElection.

The goal is to reduce code in SummaryManager and add tests for the summarizer client election logic.

[msfluid-bot]

■ @fluidframework/base-host: No change

Metric Name	Baseline Size	Compare Size	Size Diff
main.js	179.12 KB	179.12 KB	■ No change
Total Size	179.12 KB	179.12 KB	■ No change

⯅ @fluid-example/bundle-size-tests: +459 Bytes

Metric Name	Baseline Size	Compare Size	Size Diff
container.js	208.14 KB	208.59 KB	⯅ +459 Bytes
map.js	48.39 KB	48.39 KB	■ No change
matrix.js	146.8 KB	146.8 KB	■ No change
odspDriver.js	196.86 KB	196.86 KB	■ No change
odspPrefetchSnapshot.js	27.7 KB	27.7 KB	■ No change
sharedString.js	163.19 KB	163.19 KB	■ No change
Total Size	791.07 KB	791.52 KB	⯅ +459 Bytes

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Baseline commit: 6e977e8

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