Documentation for creating `import.tf` is outdated, missing `--generate-import-block`

https://learn.microsoft.com/en-us/azure/developer/terraform/azure-export-for-terraform/select-custom-resources#using-terraform-import-blocks contains faulty instructions for generating `import.tf`
The page instructs to use the `--generate-mapping-file` but it is not working.

A new `--generate-import-block` was added in https://github.com/Azure/aztfexport/pull/516 and it appears to work better instead.

Start with the Azure documentation page linked in the issue and compare its --generate-mapping-file instructions with the --generate-import-block option added in pull request #516. Update the import.tf generation guidance to use the working option, then verify that the documented steps produce the intended import.tf.

Written by the indexing model from the issue text.