feat: add hasField method for use with structs

[mbezhanov]

Description

Closes #60

Changes

The PR introduces a hasField method to the reflect registry, to address the use case explained in #60.

Checklist

• I have read the CONTRIBUTING.md document.
• My code follows the code style of this project.
• I have added tests to cover my changes.
• All new and existing tests passed.
• I have updated the documentation accordingly.
• This change requires a change to the documentation on the website.

[42atomys]

Hello @mbezhanov,

Thank you for your first contribution to Sprout! 🌱 💜

I’ve made a few changes:

• Not relevant changes: Reordered functions in the file, added tests and examples.
• Relevant change: To align with Go template conventions, I swapped the src and name arguments to allow writing with a pipe.

For example:

{{ .struct | hasField "boo" }}

Your proposals have been accepted and will be merged soon. You can start using them with the main branch; the functions will be included in the next release 🎉