refactor: Fix outstanding Style & Linter Issues

[dciborow]

Description

This fixes the following pylint issues.

-  FAIL - HIGH severity: faulty_help_example_parameters_rule
    Help-Entry: `partnercenter marketplace offer submission publish` - 
    There is a violation:
    "az partnercenter marketplace offer submission publish --offer-id MyOfferId  --submission-id 11521167929065" is not a valid command.
    the following arguments are required: --target.

Pylint
************* Module azext_partnercenter.clients.plan_listing_client
partnercenter/azext_partnercenter/clients/plan_listing_client.py:48:0: C0303: Trailing whitespace (trailing-whitespace)
partnercenter/azext_partnercenter/clients/plan_listing_client.py:65:0: C0303: Trailing whitespace (trailing-whitespace)
************* Module azext_partnercenter.clients.offer_submission_client
partnercenter/azext_partnercenter/clients/offer_submission_client.py:20:55: W0212: Access to a protected member _resource of a client class (protected-access)
partnercenter/azext_partnercenter/clients/offer_submission_client.py:25:56: W0212: Access to a protected member _resource of a client class (protected-access)
partnercenter/azext_partnercenter/clients/offer_submission_client.py:30:67: W0212: Access to a protected member _resource of a client class (protected-access)
partnercenter/azext_partnercenter/clients/offer_submission_client.py:33:4: R0201: Method could be a function (no-self-use)
************* Module azext_partnercenter.clients._product_ingestion_api_client
partnercenter/azext_partnercenter/clients/_product_ingestion_api_client.py:151:30: C0303: Trailing whitespace (trailing-whitespace)
partnercenter/azext_partnercenter/clients/_product_ingestion_api_client.py:152:0: W0311: Bad indentation. Found 11 spaces, expected 12 (bad-indentation)
partnercenter/azext_partnercenter/clients/_product_ingestion_api_client.py:13:0: W0611: Unused ResourceTarget imported from azext_partnercenter.vendored_sdks.production_ingestion.models (unused-import)
partnercenter/azext_partnercenter/clients/_product_ingestion_api_client.py:13:0: W0611: Unused TargetType imported from azext_partnercenter.vendored_sdks.production_ingestion.models (unused-import)
************* Module azext_partnercenter.operations.marketplace_offer_submission.custom
partnercenter/azext_partnercenter/operations/marketplace_offer_submission/custom.py:17:0: C0304: Final newline missing (missing-final-newline)
partnercenter/azext_partnercenter/operations/marketplace_offer_submission/custom.py:6:0: W0611: Unused TargetType imported from azext_partnercenter.models (unused-import)

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Your code has been rated at 9.92/10 (previous run: 10.00/10, -0.08)

Pylint: FAILED

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[kevinhillinger]

Created issue #187 based on discussion in this PR.

[kevinhillinger]

approved.