feat(otel): use new observability api for otel/serilog implementations

[stijnmoreels]

Use a new interface called IObservability to place traces/metrics away from the ILogger interface. This is the result of the discussion #587 . This PR provides an implementation for both OpenTelemetry and Serilog to showcase in a single go the possible abstraction and to ease the migration from Serilog ➡️ OpenTelemetry.

No feature documentation updates are made yet, as this will require a refactoring exercise by itself.

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[fgheysels]

I'm trying to wrap my head around this to see how I could use / play with it.

[fgheysels]

I'm trying to wrap my head around this to see how I could use / play with it.

Ok, I created a small console app which looks like this:

internal class Program
{
    static void Main(string[] args)
    {
        var builder = Host.CreateApplicationBuilder(args);

        builder.Services.AddOpenTelemetry().UseAzureMonitor(o => o.ConnectionString = "InstrumentationKey=....").UseObservability();

        builder.Services.AddHostedService<Worker>();

        var app = builder.Build();

        app.Run();
    }
}

public class Worker : BackgroundService
{
    private readonly IObservability _observability;

    public Worker(IObservability observability)
    {
        _observability = observability;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        var workerMetric = _observability.RecordMetric("worker_stuff");

        while (!stoppingToken.IsCancellationRequested)
        {
            Console.WriteLine($"Worker running at: {DateTime.Now}");
            workerMetric.WithValue(Random.Shared.Next(1, 15));
            await Task.Delay(1000, stoppingToken);
        }
    }
}

Metric is being registered