Fix stale Azure Container Instance examples

[samrusani]

Summary

• remove AzureContainerInstanceJob examples that no longer work in Prefect 3
• replace them with the supported Azure Container Instance work-pool and worker commands
• clarify that the remaining AzureContainerInstanceJobResult type is retained only for compatibility

AzureContainerInstanceJob was removed from prefect-azure, but the package README and module docstring still imported and invoked it. This left users with examples that fail against the current package. The updated examples now point to the implemented azure-container-instance worker path.

Related to #22028. This intentionally does not close the issue because the broader Azure Container Apps/jobs feature request remains open and is outside this documentation-only change.

Validation

• focused Ruff check and format check on container_instance.py
• Python byte-compilation of container_instance.py
• focused pre-commit hooks for Ruff, codespell, and documentation formatting
• current CLI help verified for both worker commands
• git diff --check

No runtime tests were added because this changes only a README and source docstrings. The generated API-reference page was not edited directly; it is generated from the corrected source docstring.

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • The related issue is linked above but is deliberately not closed because its broader feature request remains unresolved.
• If this is a complex change, a maintainer has confirmed the proposed approach on the linked issue.
  • Not applicable; this is a narrow documentation correction.
• If this pull request adds or changes functionality, it includes tests or explains why tests are not needed.
  • No functionality changes; validation is documented above.
• If this pull request changes user-facing behavior, it updates documentation or explains why documentation is not needed.
  • This change corrects the user-facing documentation itself.
• If this pull request removes docs files, it includes redirect settings in mint.json.
  • No documentation files are removed.
• If this pull request adds functions or classes, it includes helpful docstrings.
  • No functions or classes are added.