feat: Add support for x-www-form-urlencoded requests to rv.ValidateBody

[heyztb]

Fixes

Fixes #137

This PR adds support for x-www-form-urlencoded requests to the ValidateBody method on the RequestValidator struct. Previously, only JSON requests would be handled properly.

Checklist

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

[claudiachua]

Hi @heyztb , I had to revert this PR as you were trying to merge to main instead of the rc branch. Have included your changes here