[12.x] docs: add semantic commits guide for framework contributions

[mubbi]

This pull request updates the contributions.md file to introduce guidelines for using semantic commits. The changes emphasize adherence to the Conventional Commits specification and provide instructions for setting up commit message linting locally.

Enhancements to contribution guidelines:

• Added a new section, Semantic Commits, to the table of contents in contributions.md.
• Introduced detailed guidelines for semantic commits, including the commit message format, valid types, example messages, and instructions for setting up commit message linting using a Git hook.

Link to commitlint Pull Request: laravel/framework#56443

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If applicable, please consider releasing your code as a package so that the community can still take advantage of your contributions!

[mubbi]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If applicable, please consider releasing your code as a package so that the community can still take advantage of your contributions!

Thanks for the feedback!

Totally understand the need to keep the framework lean and maintainable. To make this functionality available to the community, I've published it as a standalone Laravel package: laravel-commit-lint.
It provides an easy way to enforce semantic commit messages in Laravel projects using a simple git hook.

Hope it’s helpful to others! Feedback and contributions are welcome.