Permissions required not clearly documented.

**Describe the bug**
When DVT stores validation results in BigQuery or GCS or retrieves secrets using the secret manager, the permissions required by the user/service account are not clearly documented. These should be documented.

There is documentation of permissions required to store validation results in BigQuery in [BigQuery connection](https://github.com/GoogleCloudPlatform/professional-services-data-validator/blob/develop/docs/connections.md#if-you-plan-to-store-validation-results-in-bigquery) section. DVT users don't need to set up a connection to store validation results in BigQuery. They can specify project.dataset.table. There is no documentation about permissions required for GCS and secret manager.

This detail belongs in the [Running Validations](https://github.com/GoogleCloudPlatform/professional-services-data-validator?tab=readme-ov-file#running-validations) section