Issue 3159: Added support for AzureStackHub and Azure private cloud identification

[schaafito]

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Added support for AzureStackHub and private Azure cloud environments by updating the getCloudConfiguration() logic to fall-through to the kubernetes cloud-provider-azure module logic for identifying private cloud environments. This fall-through supports both AZURE_RESOURCE_MANAGER_ENDPOINT cloud discovery as well as AZURE_ENVIRONMENT_FILEPATH discovery.

The private cloud logic can (partially) be tested on any Azure environment by setting the AZURE_CLOUD_NAME to AZURESTACKCLOUD and providing a valid azurestackcloud.json configuration file as documented here. You can set the cloud endpoints to valid endpoints for a public cloud offering to test fallthrough logic.

The bulk of the documentation updates will need to be done on the velero-plugin-for-microsoft-azure project which I plan during the PR cycle to recompile the plugin with these changes. The proposed documentation changes can be seen on my branch

I provided unit tests for both endpoint and filepath cloud discovery, as well as tested in my own Azure environments to confirm functionality.

Note: This feature requires golang1.23 support so I bumped those as well. I see an open PR #8717 which I suspect will need to be merged before this.

Does your change fix a particular issue?

Fixes #3159

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• Accepted the DCO. Commits without the DCO will delay acceptance.
• Created a changelog file (make new-changelog) or comment /kind changelog-not-required on this PR.
• Updated the corresponding documentation in site/content/docs/main.