feat: add aws sns metadata schema

[Eileen-Yu]

Description

Add metadata schema for aws sns binding.

Issue reference

#3432

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation / Created issue in the https://github.com/dapr/docs/ repo: dapr/docs#[issue number]

Lint failing

[yaron2]

Thanks, please see failing lint

[Eileen-Yu]

added missing endpoint field, run make check-component-metadata and works fine locally... guess we may also want to add that field to docs here: https://docs.dapr.io/reference/components-reference/supported-bindings/sns/

[Eileen-Yu]

guess this one is ready, the CI failure seems unrelated to this PR?

[marcduiker]

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