[master] Deprecate proxmox cloud

[I3urny]

What does this PR do?

Deprecate proxmox cloud

What issues does this PR fix or reference?

Fixes: #64224

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• Docs
• Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• Tests written/updated

Commits signed with GPG?

No

Please review Salt's Contributing Guide for best practices.

See GitHub's page on GPG signing for more information about signing commits with GPG.

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[whytewolf]

I know it seems silly since this is a deprecation. but the added utils decorator does need a test.

[Ch3LL]

https://docs.saltproject.io/en/latest/topics/development/deprecations.html

The version should be 3009. "A deprecation warning should be in place for at least two major releases"