Only initialize listeners once

[Tratcher]

Fixes #90779

AddMetrics uses an options validation workaround to initialize the MetricsSubscriptionManager and IMetricsListeners. However, if AddMetrics is called multiple times, it will do the initialization multiple times. IMetricsListener implementations may not be expecting that.

This adjusts the options validation logic to make sure initialize is only called once.

Suggest backporting to release/8.0 (but not RC1).

[JamesNK]

Does services.AddOptions<NoOpOptions>().ValidateOnStart(); register anything multiple times?

[Tratcher]

Does services.AddOptions<NoOpOptions>().ValidateOnStart(); register anything multiple times?

This bit might, but since it's a set operation it doesn't cause duplicate work later.

runtime/src/libraries/Microsoft.Extensions.Options/src/OptionsBuilderExtensions.cs

Lines 28 to 36 in 9f8c01d

	optionsBuilder.Services.AddTransient<IStartupValidator, StartupValidator>();
	optionsBuilder.Services.AddOptions<StartupValidatorOptions>()
	.Configure<IOptionsMonitor<TOptions>>((vo, options) =>
	{
	// This adds an action that resolves the options value to force evaluation
	// We don't care about the result as duplicates are not important
	vo._validators[(typeof(TOptions), optionsBuilder.Name)] = () => options.Get(optionsBuilder.Name);
	});

The types aren't public so I can't do it myself.

[Tratcher]

/backport to release/8.0

[github-actions]

Started backporting to release/8.0: https://github.com/dotnet/runtime/actions/runs/5941582906