Introduce ResilienceStrategyRegistry

[martintmk]

The issue or feature being addressed

#1084

Details on the issue fix or feature implementation

Registry allows registration and retrieval of strategies:

var registry = new ResilienceStrategyRegistry<string>();
var strategy = new ResilienceStrategyBuilder().AddTimeout(TimeSpan.FromSeconds(10));

registry.TryAdd("timeout-strategy", strategy);
registry.Get("timeout-strategy");

Or builders:

var registry = new ResilienceStrategyRegistry<string>();
registry.AddBuilder("timeout-strategy", (key, builder) => builder.AddTimeout(TimeSpan.FromSeconds(10));
registry.Get("timeout-strategy"); // strategy is dynamically created on-demand

The more advanced scenarios allow multi-instance support where one builder is repeatedly used to create multiple strategies. Registry then caches each of these strategies individually. We need this functionality to allow having distinct circuit breaker instances that are cached by composite keys.

Typical scenario for this is having HttpClient that sends requests to a different server across multiple geo-locations. We want to have a different circuit breaker instances assigned.

var registry = new ResilienceStrategyRegistry<StrategyId>(new ResilienceStrategyRegistryOptions<StrategyId>
{
    StrategyComparer = StrategyId.Comparer,
    BuilderComparer = StrategyId.BuilderComparer
});

registry.TryAddBuilder(StrategyId.Create("my-pipeline"), (id, builder) => builder.AddCircuitBreaker());

// access the strategy
registry.Get(StrategyId.Create("my-pipeline", "instance-A"));
registry.Get(StrategyId.Create("my-pipeline", "instance-B"));

In the follow-up (#1087) I would like to introduce Polly.Hosting or Polly.DependencyInjection project that integrates the ResilienceStrategyRegistry into the DI and allows defining the strategies at startup using IServiceCollection. That way, the core infra will be done and we can focus fully on strategies.

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

[martintmk]

@geeknoid We can consider moving this to the core API as we would propably have to copy-paste this piece to our codebase. This struct allows:

• Isolation of strategies by the type of the result they are handling.
• Multi-instance support.

cc @martincostello

[codecov-commenter]

Codecov Report

Merging #1085 (5090a18) into main (94b309d) will increase coverage by 0.20%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main    #1085      +/-   ##
==========================================
+ Coverage   74.83%   75.04%   +0.20%     
==========================================
  Files         170      173       +3     
  Lines        4208     4243      +35     
  Branches      787      790       +3     
==========================================
+ Hits         3149     3184      +35     
  Misses        854      854              
  Partials      205      205              

Flag	Coverage Δ
linux	?
macos	75.04% <100.00%> (+0.20%)	⬆️
windows	?

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Impacted Files	Coverage Δ
.../Polly.Core/Registry/ResilienceStrategyProvider.cs	100.00% <100.00%> (ø)
.../Polly.Core/Registry/ResilienceStrategyRegistry.cs	100.00% <100.00%> (ø)
...Core/Registry/ResilienceStrategyRegistryOptions.cs	100.00% <100.00%> (ø)

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[geeknoid]

Please document all the default values of the properties and what they do.

[geeknoid]

Suggested change

	/// The ResilienceStrategyRegistry class provides a way to organize and manage multiple resilience strategies
	/// This class provides a way to organize and manage multiple resilience strategies