Secrets Manager: align "acls" with provider-wide "acl" naming

[mrcljnff1]

Problem description

stackit_secretsmanager_instance currently uses acls, while other STACKIT provider resources use acl for the same concept.

Examples:

• stackit_secretsmanager_instance -> acls
• stackit_postgresflex_instance -> acl
• stackit_observability_instance -> acl

This creates an inconsistent provider experience.

Proposed solution

Introduce acl as the canonical attribute name for stackit_secretsmanager_instance.

Preferred implementation:

• add acl
• keep acls temporarily for backward compatibility
• mark acls as deprecated
• reject configurations that set both acl and acls
• update examples and generated docs to use acl

Alternative solutions (optional)

Keep acls as-is and explicitly document it as a special case. I think this is the weaker option because it preserves the inconsistency.

Additional information

I am reporting this as a consistency/enhancement topic, not as a security issue.

[Manuelvaas]

Hi @mrcljnff1,
thank you for reporting this issue. We will take a look at it.