add sse_c_key from S3 object storage properties config to list of sensitive values

[rriemann]

Summary

Some logs (e.g. occ config:list) show encryption keys in clear. Let's redact this value!

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[github-actions]

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[welcome]

Thanks for your first pull request and welcome to the community! Feel free to keep them coming! If you are looking for issues to tackle then have a look at this selection: https://github.com/nextcloud/server/issues?q=is%3Aopen+is%3Aissue+label%3A%22good+first+issue%22

[skjnldsv]

/backport to stable30

[skjnldsv]

/backport to stable29