Follow Up: Make '--platform' argument mandatory in CLI

[parthosa]

Fixes #1472.

This PR ensures that the --help output for the CLI command reflects the --platform parameter as mandatory.

Current Behavior

Running the command spark_rapids qualification -- --help incorrectly shows the platform argument as optional:

 -p, --platform=PLATFORM
        Type: Optional[str]
        Default: None
        defines one of the following "onprem", "emr", "dataproc", "dataproc-gke", "databricks-aws", and "databricks-azure".

After this PR

    -p, --platform=PLATFORM (required)
        Type: str
        Defines one of the following: "onprem", "emr", "dataproc", "dataproc-gke", "databricks-aws", and "databricks-azure".

[amahussein]

Thanks @parthosa
LGTME