fix: fix validateExpressRequest issue

[shwetha-manvinkurke]

Fixes

This PR fixes issue when the validateExpressRequest is used for webhook validation when the content-type is application/json.

Note: We expect the request.rawBody populated for the validation in this case.

Fixes #657

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
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

[thinkingserious]

🥇