Add builder pattern support for event response types

[FullyTyped]

Add derived builders to events.
Builders are conditionally compiled with the "builders" feature flag.

📬 Issue #, if available: #1060

🔏 By submitting this pull request

• I confirm that I've ran cargo +nightly fmt.
• I confirm that I've ran cargo clippy --fix.
• I confirm that I've made a best effort attempt to update all relevant documentation.
• I confirm that my contribution is made under the terms of the Apache 2.0 license.

[FullyTyped]

Hi folks, so with this PR we aim to address the issues that were introduced when we tagged events as non-exhaustive.

@lmammino @jeastham1993 @ikai104 your feedback is appreciated. I looked at the examples you've posted in #1060 and added before and after in the examples folder.