chore: add signed webhook test for multi event payload

[shwetha-manvinkurke]

Add example to show how to process payloads with multiple events for signed webhook verification.

Note: The webhook verification logic itself works fine with the raw request body in the example shown here.

Fixes #1238

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch

[childish-sambino]

Should link this to the open issue.