SIANXSVC-1186: Terminate application after writing metadata

[nachtjasmin]

Closes SIANXSVC-1186

Proof of concept

In order to test that the changes work, the following code was used:

using Anexia.E5E.Extensions;
using Anexia.E5E.Functions;

var host = Host.CreateDefaultBuilder(args)
	.UseAnexiaE5E(_ => {}) // ignore the setup this time
	.UseConsoleLifetime()
	.Build();

await host.StartAsync();

await Task.Delay(10000); // imitate a long startup task

await host.WaitForShutdownAsync();

If I run this code with dotnet run metadata, the application prints the metadata and terminates immediately.

Caveats

Unfortunately, Environment.Exit would also end the test processes, therefore it had to be abstracted a bit.

[PatrickTaibel]

This does not work with the current metadata fetching implementation in e5e. Calling the metadata command outputs the expected JSON in time but the binary keeps running until the initialization is done.
e5e only starts to interpret the stdout after the binary exited with status code 0 to ensure that the metadata was generated successfully.
Therefore, the current way would not work in the following conditions:

• long running initialization code
• exceptions occurring (e.g. due to missing network connections)

[PatrickTaibel]

Metadata fetching now works as expected.

FYI this PR is not based on the current main, so the response result is not fixed yet. I'm missing permissions on this repo else I would have pushed my local rebase.