chore: migrate to stackit-sdk-go v1api and update API calls

[jojomo96]

This pull request updates the Stackit DNS provider integration to use the new v1api client from the stackit-sdk-go library, and refactors the codebase to work with the updated API types and structures. The changes remove the use of pointer-based fields in favor of direct values, streamline record and zone handling, and update all relevant tests accordingly.

Key changes include:

Migration to v1api client and updated types:

• Switched all imports from github.com/stackitcloud/stackit-sdk-go/services/dns to github.com/stackitcloud/stackit-sdk-go/services/dns/v1api across the codebase and tests to use the updated API client. [1] [2] [3] [4] [5]
• Updated the Go module dependency to use stackit-sdk-go/services/dns v0.19.2, which includes the new v1api.

Refactoring for new API data structures:

• Refactored all usages of DNS zone and record set fields to use direct values instead of pointers (e.g., zone.Id instead of *zone.Id, zone.DnsName instead of *zone.DnsName). [1] [2] [3] [4]
• Updated payload construction functions and their usages to match the new API types, removing unnecessary pointer wrapping and using direct assignment for fields like Name, Type, Ttl, and Records. [1] [2]

API method usage updates:

• Changed API method calls to use the new DefaultAPI interface provided by v1api, and adjusted parameter passing to use direct values. [1] [2] [3]
• Updated logging and error handling to reflect the new types and method signatures. [1] [2] [3]

Test updates for new types and structures:

• Refactored all test fixtures and assertions to use the new value-based types for zones, record sets, and their fields. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

These changes collectively modernize the Stackit DNS provider codebase, ensuring compatibility with the latest SDK version and improving code clarity and maintainability.