Support for "Ambient" Credentials i.e. RRSA and Worker Roles

[onelapahead]

• Fixes from testing #29
• Adds logging via klog/v2 to help w/ debugging nil pointers and bad credentials
• Builds with Go 1.24 and latest Alpine, but only requires Go 1.21 for now
• Tested w/ RAM worker roles (re-using ExternalDNS worker role described here: https://www.alibabacloud.com/help/en/ack/ack-managed-and-ack-dedicated/user-guide/use-externaldns-to-configure-external-dns-servers)

Now you can just set the webhook config like so:

        dns01:
          webhook:
            config:
              regionId: us-west-1
            groupName: example.com
            solverName: alidns-solver

And it configures the SDK to use "ambient" credentials which might come from env vars / secrets (RRSA flow) or from trying the worker role flow. Can try it out at ghcr.io/onelapahead/alidns-webhook:latest.