Add o3de/o3de to game-engines

[MatiasDuhalde]

Please confirm this pull request meets the following requirements:

• I followed the contributing guidelines: https://github.com/github/explore/blob/main/CONTRIBUTING.md.
• I am not the sole author or employee of a company who created the topic or collection I'm changing.

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Editing an existing topic or collection

I'm suggesting these edits to an existing topic or collection:

• Image (and my file is *.png, square, dimensions 288x288, size <= 75 kB)
• Content (and my changes are in index.md)

O3DE is a free and open source engine, successor to AWS's Lumberyard game engine. While still in early stages, it has a growing community and receives constant updates. The next release is scheduled for Oct 9, 2023.

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[ipc103]

👍 ❤️ Looks good, thank you for the contribution!