Resilience telemetry API

[martintmk]

The issue or feature being addressed

Closes #1112

Details on the issue fix or feature implementation

This PR enables the real telemetry for Polly.Core by calling the EnableTelemetry extension.

API Usage:

var options = new ResilienceStrategyTelemetryOptions
{
    LoggerFactory = NullLoggerFactory.Instance
};

// configure custom enrichers
options.Enrichers.Add(context =>
{
    context.Tags.Add(new KeyValuePair<string, object?>("my-custom-dimension", "some-value"));
});
        
// enable telemetry
var builder = new ResilienceStrategyBuilder().EnableTelemetry(options);

The telemetry is automatically enabled for resilience strategies added using IServiceCollection.

Confirm the following

• I started this PR by branching from the head of the default branch
• I have targeted the PR to merge into the default branch
• I have included unit tests for the issue/feature
• I have successfully run a local build

[martincostello]

Suggested change

	foreach (var pair in context.Tags)
	{
	tags.Add(pair.Key, pair.Value);
	}
	if (context.Tags.Count > 0)
	{
	foreach (var pair in context.Tags)
	{
	tags.Add(pair.Key, pair.Value);
	}
	}