Add support for `--profile` flag for choosing AWS profile

Currently, all `boto3` clients are initiated without specifying the AWS profile name. Hence, the `default` profile will be used.

Adding the `--profile` flag would significantly improve the handiness of the CLI because it is very common to switch the profile frequently during development (for example, changing the target environment between `dev` and `prod` by switching the AWS profile).

Start by tracing the CLI argument handling and the boto3 client initialization points in the repository. Add the requested --profile option so the selected AWS profile is used instead of the default, then verify the CLI still packages, deploys, and runs EMR Serverless Spark jobs correctly with that profile.

Written by the indexing model from the issue text.