CloudWatch: Add missing GameLift metrics

[fridgepoet]

What is this feature?

This adds metrics for standard GameLift metrics which are currently not available

Originally #72805 by @Ciara-Cloud
Thanks also to @jangaraj for great suggestions on the original PR

Who is this feature for?

Users of CloudWatch

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.

[CLAassistant]

All committers have signed the CLA.

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