Move default value for --rpc-pubsub-notification-threads to CLI #162

Job	Run time
ios (macos-11, aarch64-apple-ios)	6m 10s
android (ubuntu-20.04, x86_64-linux-android)	2m 53s
ios (macos-11, x86_64-apple-ios)	6m 9s
android (ubuntu-20.04, aarch64-linux-android)	2m 57s
ios (macos-11, aarch64-apple-darwin)	11m 36s
android (ubuntu-20.04, i686-linux-android)	2m 54s
ios (macos-11, x86_64-apple-darwin)	8m 14s
android (ubuntu-20.04, armv7-linux-androideabi)	3m 15s
error_reporting	0s
	44m 8s

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