Introduce ResilienceStrategyBuilder.InstanceName and use it in telemetry

[martintmk]

Details on the issue fix or feature implementation

The main purpose of InstanceName is to differentiate between multiple instances that have the same BuilderName. It defaults to null.

Previously, we had the strategy-key dimension that was not easy to configure using the API. It was also ambiguous with strategy-name and strategy-type.

Now, every resilience event has the following dimension that can identify by wich resilience strategy is was produced:

• builder-name: the name of the builder, when using the AddResilienceStrategy extension this becomes the key identifier
• builder-instance: the instance of the builder. Generally, it's null and consumer can set it up manually or configure the InstanceNameFormatter delegate to fill it when using complex keys (Demonstrate how to create dynamic strategies with complex keys #1366).
• strategy-type: hard-coded strategy type (Retry, Hedging, Timeout)
• strategy-name: consumer can set it up to add more details to the telemetry. Defaults to null.

As a part of this change I have also simplified the log messages to make them shorter.

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