Adds option to switch provider test contract source

What does this MR do and why?

This change allows the provider test to fetch the contract from a local source or from a pact broker depending on the environment variable set.

Changes include:

1. Updating all provider specs to use PublishContractHelper.
2. Updating all provider specs to use ContractSourceHelper.
3. Moved spec/contracts/provider/pact_helpers/project/pipeline_schedule/update_pipeline_schedule_helper.rb as it wasn't following the correct folder structure convention.

Related: #380899 (closed)

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