Add S3 snapshot repository settings

[moesterheld]

Description

• Prepares snapshot repository settings to have common settings and repository type specific settings
• Adds missing settings from https://docs.opensearch.org/latest/api-reference/snapshots/create-repository/
• Fixes setting name read_only to readonly
• Fixes cleanup in snapshot test
• Adds s3 repository settings from https://docs.opensearch.org/latest/api-reference/snapshots/create-repository/
• Adds test for s3 repository

Issues Resolved

part of opensearch-project/opensearch-java#1202

if the general approach is fine, I will then add the additional prs for gcs, hadoop and azure

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