Ensure pg_rewind will be used and won't fail for Patroni

What does this MR do?

This MR ensures that:

1. For Patroni settings that can be defined in both patroni.yaml and DCS, Omnibus first updates the DCS and the reloads Patroni service. This will ensure that and attribute such as use_pg_rewind will be properly reflected in cluster config.
2. Change file mode for server.crt and server.key to 0600 when patroni['use_pg_rewind'] = true to ensure that pg_rewind will not fail. For more details see: https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/5842#note_128209929

Related issues

Part of #5746 (closed)

Checklist

See Definition of done.

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Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
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• Tests added
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