ServiceGroup should support dynamically adding Services while its running

[fabianfett]

There are scenarios in which users need a running Service in order to retrieve data. This data shall then be used to spawn another Service.

An example for this could be querying AWS SSM for a secret that is then used inside a Lambda.

I imagine the code to look something like this:

import Soto
import SotoSSM

enum MyLambda {
    static func main() async throws {
        let awsClient = AWSClient()
        let ssmClient = SSMClient(awsClient)

        try await withTaskGroup { taskGroup in
            let serviceGroup = ServiceGroup([awsClient])
            taskGroup.addTask {
                try await serviceGroup.run()
            }

            let mySecret = try await ssmClient.getSecret()

            let runtime = LambdaRuntime { (event: Request, context) in
                // use mySecret
            }

            // add runtime to already running serviceGroup.
            serviceGroup.add(runtime)
        }
    }
}

[FranzBusch]

I think we can totally do that and be able to add dynamic services to the group. I was briefly thinking if having dependency between services during startup could be used here. I think it could but it would become awkward to spell. So yeah great feature requests!