Fix MeasurementNotificationService binding

[tortmayr]

What it does

Ensure that the MeasurementNotificationService identifer is bound in singleton scope.
Otherwise it can only be injected once i.e. if another service injects the MeasurementNotificationService
it would fail with an error like:

channel.ts:283 Uncaught (in promise) Error: Another channel with the id '/services/measurement-notification' is already open.
    at ChannelMultiplexer.open (channel.ts:283:19)
    at ServiceConnectionProvider.openChannel (service-connection-provider.ts:137:58)

How to test

Follow-ups

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[sdirix]

Looks good to me!