[36500] Allow to specify single DNS server when using Customer Manage Active Directory for RDS MSSQL

[kostasns]

Description

Currently when working with Customer Managed Active Directory it is not possible to provide a single domain controller IP by providing it twice, see reference below.
This PR changes type for 'domain_dns_ip' from Set to List to allow this option.

Relations

Closes #36500

References

https://docs.aws.amazon.com/AmazonRDS/latest/APIReference/API_ModifyDBInstance.html#API_ModifyDBInstance_RequestParameters

DomainDnsIps.member.N
The IPv4 DNS IP addresses of your primary and secondary Active Directory domain controllers.

Constraints:
Two IP addresses must be provided. If there isn't a secondary domain controller, use the IP address of the primary domain controller for both entries in the list.

Output from Acceptance Testing

I'm unable to run acc tests, this is a best effort implementation.

[github-actions]

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[github-actions]

Welcome @kostasns 👋

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