BigQuery normalization: make credentials json optional

[ChristopheDuong]

What

Closes #4199

How

Describe the solution

Recommended reading order

1. x.java
2. y.python

Pre-merge Checklist

Expand the relevant checklist and delete the others.

New Connector

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• Unit & integration tests added and passing. Community members, please provide proof of success locally e.g: screenshot or copy-paste unit, integration, and acceptance test output. To run acceptance tests for a Python connector, follow instructions in the README. For java connectors run ./gradlew :airbyte-integrations:connectors:<name>:integrationTest.
• Code reviews completed
• Documentation updated
  • Connector's README.md
  • docs/SUMMARY.md
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  • docs/integrations/README.md
  • airbyte-integrations/builds.md
• PR name follows PR naming conventions
• Connector added to connector index like described here

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If this is a community PR, the Airbyte engineer reviewing this PR is responsible for the below items.

• Create a non-forked branch based on this PR and test the below items on it
• Build is successful
• Credentials added to Github CI. Instructions.
• /test connector=connectors/<name> command is passing.
• New Connector version released on Dockerhub by running the /publish command described here

Updating a connector

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• Grant edit access to maintainers (instructions)
• Secrets in the connector's spec are annotated with airbyte_secret
• Unit & integration tests added and passing. Community members, please provide proof of success locally e.g: screenshot or copy-paste unit, integration, and acceptance test output. To run acceptance tests for a Python connector, follow instructions in the README. For java connectors run ./gradlew :airbyte-integrations:connectors:<name>:integrationTest.
• Code reviews completed
• Documentation updated
  • Connector's README.md
  • Changelog updated in docs/integrations/<source or destination>/<name>.md including changelog. See changelog example
• PR name follows PR naming conventions
• Connector version bumped like described here

Airbyter

If this is a community PR, the Airbyte engineer reviewing this PR is responsible for the below items.

• Create a non-forked branch based on this PR and test the below items on it
• Build is successful
• Credentials added to Github CI. Instructions.
• /test connector=connectors/<name> command is passing.
• New Connector version released on Dockerhub by running the /publish command described here

Connector Generator

• Issue acceptance criteria met
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• If adding a new generator, add it to the list of scaffold modules being tested
• The generator test modules (all connectors with -scaffold in their name) have been updated with the latest scaffold by running ./gradlew :airbyte-integrations:connector-templates:generator:testScaffoldTemplates then checking in your changes
• Documentation which references the generator is updated as needed.

[ChristopheDuong]

/test connector=bases/base-normalization

🕑 bases/base-normalization https://github.com/airbytehq/airbyte/actions/runs/1136342289
✅ bases/base-normalization https://github.com/airbytehq/airbyte/actions/runs/1136342289

[marcosmarxm]

Awesome!

[ChristopheDuong]

/publish connector=bases/base-normalization

🕑 bases/base-normalization https://github.com/airbytehq/airbyte/actions/runs/1138641771
✅ bases/base-normalization https://github.com/airbytehq/airbyte/actions/runs/1138641771