feat: add Azure Container Linux CVM SIG config

[Ankita Pareek (Ankita13-code)]

What this PR does / why we need it:

Adds AgentBaker SIG configuration for the Azure Container Linux Confidential VM Gen2 distro, aks-acl-cvm-gen2, so AKS can resolve the distro to its Azure Linux gallery image.

Changes:

• Adds the AKSACLCVMGen2 distro constant and includes it in AKSDistrosAvailableOnVHD.
• Registers the distro in the containerd, Gen2, and Azure Container Linux availability lists.
• Adds the SIGACLCVMGen2ImageConfigTemplate and Azure Linux SIG config-map entry.
• Uses the generated SIG definition aclgen2CVMSpecialized: the release template generates aclgen2CVM, then ensure_sig_image_name_linux appends Specialized for CVM images.
• Adds unit-test coverage for maintained-image registration, cloud-specific SIG resolution, ACL classification, and version-override resolution.

Validation:

• go test ./pkg/agent/...

Related work and dependency:

• Depends on ACL CVM image-build support in feat: add ACL CVM support #9283. This PR should remain in draft until feat: add ACL CVM support #9283 is merged.
• This change must remain aligned with the AKS-RP distro constant aks-acl-cvm-gen2.

Which issue(s) this PR fixes:

Fixes #

[github-actions]

Windows Unit Test Results

  3 files   13 suites   48s ⏱️
404 tests 404 ✅ 0 💤 0 ❌
407 runs  407 ✅ 0 💤 0 ❌

Results for commit f1ab4c9.

♻️ This comment has been updated with latest results.

[Copilot]

Pull request overview

Adds AgentBaker SIG configuration for Azure Container Linux CVM Gen2.

Changes:

• Registers the new distro and capability classifications.
• Adds Azure Linux SIG resolution and tests.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
pkg/agent/datamodel/types.go	Defines and enables the distro.
pkg/agent/datamodel/sig_config.go	Adds classifiers and SIG mapping.
pkg/agent/datamodel/sig_config_test.go	Tests SIG registration and resolution.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.