CBG-5227: background metadata migration task

[gregns1]

CBG-5227

Add the legwork for a background task to manage metadata migration from the default collection to the mobile system collection.

• New MetadataMigrationManager which implements BackgroundManagerProcessI interface which follows other background managers
• Opt-in config on the db config level. New use_system_metadata_collection field on DbConfig which defaults to false
• StartOnlineProcesses will run armMetadataMigrationTask which will poll every 10 seconds the function tryStartMetadataMigration until all nodes in the cluster have applied the same db config version this node has if the dbconfig has the use_system_metadata_collection option set to true OR the bootstrap level option is true.
• tryStartMetadataMigration handles all the logic for starting migration and backs out when a node has already started the task.
• Bundles in the CCV refactor out of CBG-5406 too

Pre-review checklist

• Removed debug logging (fmt.Print, log.Print, ...)
• Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

Dependencies (if applicable)

• Link upstream PRs
• Update Go module dependencies when merged

Integration Tests

• https://jenkins.sgwdev.com/job/SyncGatewayIntegration/694/

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[github-actions]

Redocly previews

• Admin API
• Public API
• Metric API
• Diagnostic API

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[bbrks]

LGTM 👍