docs: Add endpoint to AWSConfig in readme

[schalksnyman]

What?

Add endpoint to the AWSConfig configuration. The AWS endpoint is useful to configure when testing locally e.g. against localstack.

Checklist

• [x] I have used a meaningful title for the PR.

• [x] I have described the changes I've made in the "What?" section above.

• [x] I have performed a self-review of my changes.

• [x] I have run the npm start command locally and verified that the changes look good.

• [x] I have made my changes in the docs/sources/next folder of the documentation.

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