[docs] Document available templates and boilerplates

[YourMCGeek]

Description

Add documentation for available templates and boilerplates provided by Raycast. When creating my first extension, I didn't fully know what each command template would do. This documentation update aims to provide an awareness for the available command templates. Besides it's own standalone page, I referenced the page in the Create First Extension page to hopefully increase awareness.

I tried to follow the established styles when it comes to assets, but wasn't able to create as clean screenshots or any sort of gradient like other assets. Assistance would be appreciated with this to ensure consistency across the documentation.

Screencast

CleanShot.2025-02-27.at.23.00.16.mp4

Checklist

• I read the extension guidelines
• I read the documentation about publishing
• I ran npm run build and tested this distribution build in Raycast
• I checked that files in the assets folder are used by the extension itself
• I checked that assets used in the README are located outside the metadata folder if they were not generated with our metadata tool