Support running health checks in Check method

[JamesNK]

Fixes #1963

This has a behavioral change to always run health checks when the Check method is called, and when the Watch method returns its initial results. I think the behavioral change is worth it because it stops the problem of apps calling the method before the health check publisher has published results.

Setting UseHealthChecksCache to true reverts behavior to always using cached health check publisher results.

New API:

namespace Grpc.AspNetCore.HealthChecks;

public sealed class GrpcHealthChecksOptions
{
+    public bool UseHealthChecksCache { get; set; }
}

Usage:

var services = new ServiceCollection();
services
    .AddGrpcHealthChecks(o =>
    {
        o.Services.MapService("", result => !result.Tags.Contains("exclude"));
        o.UseHealthChecksCache = true;
    });