Implement observable_object_main_actor rule

[72A12F4E]

Closes #3655

[SwiftLintBot]

	2 Warnings
⚠️	This PR introduced a violation in Alamofire: /watchOS Example/watchOS Example WatchKit Extension/Networking.swift:28:7: warning: Observable Object Main Actor Violation: ObservableObject should be annotated with @MainActor to ensure that any updates to @Published state occur on the main thread. (observable_object_main_actor)
⚠️	This PR introduced a violation in Realm: /RealmSwift/SwiftUI.swift:156:9: warning: Observable Object Main Actor Violation: ObservableObject should be annotated with @MainActor to ensure that any updates to @Published state occur on the main thread. (observable_object_main_actor)

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📖	Linting Realm with this PR took 1.53s vs 1.53s on master (0% slower)
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