Drop DelegatingResilienceStrategy

[martintmk]

The issue or feature being addressed

When writing additional tests, I realized that the DelegatingResilienceStrategy doesn't work really well when you want to share the ResilienceStrategy across different pipelines. The problem is with the mutable Next property. It also creates ambiguity when implementing a new strategy as we now have two base classes to derive from.

To fix this problem and simplify the API we are dropping DelegatingResilienceStrategy and making it an internal implementation detail that is used when we are linking multiple strategies together.

This simplifies the API surface and also removes some infra around freezing the pipelines which won't be needed anymore.

The downside is slightly slower execution; however, we should focus on clean API first.

Details on the issue fix or feature implementation

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