createServicePolicy: Convert callbacks to methods

[mcmire]

Explanation

Both RetryPolicy and CircuitBreakerPolicy from the Cockatiel library allow for listening for events using on* methods. For instance, if you have a retry policy, you can listen for when the function is retried like so:

retryPolicy.onRetry(() => {
  // ...
})

Our "service policy" allows for listening to some of the same events as well as the "degraded" event. Instead of exposing on* methods, however, createServicePolicy takes callbacks in an options bag:

createServicePolicy({
  // ...
  onRetry: () => {
    // ...
  }
)

For parity with Cockatiel — and for easier use in general — this commit changes the API so that the object that createServicePolicy returns now includes similar on* methods. This way you can say:

const policy = createServicePolicy({ ... });
policy.onRetry(() => {
  // ...
});

References

Progresses #4994.
Pre-requisite to #4990.

Changelog

(Updated in PR.)

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've highlighted breaking changes using the "BREAKING" category above as appropriate
• I've prepared draft pull requests for clients and consumer packages to resolve any breaking changes

[cryptodev-2s]

Great improvements