Revert "Follow Up: Make '--platform' argument mandatory in CLI (#1473)"

[parthosa]

Fixes #1497.

In #1472, the --platform argument was made a required parameter in Fire. In our tests, it was found that the short flag -p for platform is no longer functioning.

Upon investigation, it seems that Fire does not support short flags for required arguments.

This PR reverts the above commit and makes the platform argument optional in Fire. This change will ensure compatibility with the -p flag.

The platform argument will still be validated internally to ensure its requirement is enforced.

Case 1 : Platform not provided

spark_rapids qualification  --eventlogs "/path/to/dataproc-cpu" --verbose

STDOUT

2025-01-10 13:35:16,011 INFO spark_rapids_tools.argparser: ...applying argument case: Missing Platform argument
2025-01-10 13:35:16,012 ERROR spark_rapids_tools.argparser: Validation err: 1 validation error for QualifyUserArgModel
  Cannot run tool cmd without platform argument. Re-run the command providing the platform argument.
  Error: [type=invalid_argument, input_value=ArgsKwargs((), {'eventlog...ols_config_path': None}), input_type=ArgsKwargs]

Case 2: Platform provided by --platform and -p

spark_rapids qualification --platform dataproc --eventlogs "/path/to/dataproc-cpu" --verbose
spark_rapids qualification -p dataproc --eventlogs "/path/to/dataproc-cpu" --verbose

STDOUT

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