Add Component tutorial to Extend section.

[ShaunaGordon]

Change summary

As part of the process of moving things out of the Github Wiki and into the docs, this PR pulls the Let's Make a Component walkthrough from https://github.com/o3de/o3de/wiki/(WIP)-Walk%E2%80%90through:-Let's-create-components-in-c%E2%80%90plusplus .

TODO:

This still needs a number of things before it's ready for prime time. Any help is welcome.

• Validation - We need to walk through what's there and see if everything is still valid. Anything that isn't should be marked for updating.
• Completion - It's not completely finished. There's a section at the bottom that indicates where the tutorial has thus far stopped. We need to flesh it out.
• Transfer Images - Images are currently hosted on Github, since it was originally a Github wiki page. They need migrated into the website source and their links updated.
• Content Editing - What's there needs edited for content. Old things removed, new things added, etc.
• Style Editing/Proofreading - It's written very informally and not necessarily following our style, and it just in general needs proofread.

Submission Checklist:

• Descriptive active voice - Do descriptive sentences have a clear subject and action verb?
• Answer the question at hand - Does the documentation answer a what, why, how, or where type of question?
• Consistency - Does the content consistently follow the Style Guide?
• Help the user - Does the documentation show the user something meaningful?