Use delegates in RetryStrategyOptions

[martintmk]

The issue or feature being addressed

Contributes to #1211.

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

[codecov-commenter]

Codecov Report

Merging #1214 (b6530f0) into main (15473aa) will increase coverage by 0.06%.
The diff coverage is 100.00%.

❗ Your organization is not using the GitHub App Integration. As a result you may experience degraded service beginning May 15th. Please install the Github App Integration for your organization. Read more.

@@            Coverage Diff             @@
##             main    #1214      +/-   ##
==========================================
+ Coverage   83.93%   83.99%   +0.06%     
==========================================
  Files         280      280              
  Lines        6528     6555      +27     
  Branches     1034     1036       +2     
==========================================
+ Hits         5479     5506      +27     
  Misses        844      844              
  Partials      205      205              

Flag	Coverage Δ
linux	?
macos	83.99% <100.00%> (?)
windows	83.99% <100.00%> (+0.06%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...rc/Polly.Core/Strategy/OutcomeGenerator.TResult.cs	100.00% <ø> (ø)
src/Polly.Core/Retry/RetryResilienceStrategy.cs	100.00% <100.00%> (ø)
.../Retry/RetryResilienceStrategyBuilderExtensions.cs	100.00% <100.00%> (ø)
...c/Polly.Core/Retry/RetryStrategyOptions.TResult.cs	100.00% <100.00%> (ø)
src/Polly.Core/Retry/RetryStrategyOptions.cs	100.00% <100.00%> (ø)