fix: missing documented 'oidc_provider_arn' variable.

[fabienduhamel]

📒 Description

I added the ability to provide an external oidc_provider_arn as shown in the README but not implemented yet.

🕶️ Types of changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Documentation
• Dependencies

🔎 Review hints

You can use the module separately to check the feature:

• one usage of the module with create_oidc_provider = true
• one usage of the module with create_oidc_provider = false and oidc_provider_arn = module.<previous_usage>.oidc_provider_arn

🚨 Test instructions

Checklist

• My code follows the code style of this project.
• I have read the CONTRIBUTING document.
• Added/updated unit tests for this change
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).
• Filled out test instructions (In case there aren't any unit tests)
• I followed the existing code standards and didn't mess up the formatting.
• My change requires a change to the documentation.
• I did my best to add documentation to any public classes or methods I added.
• Included links to related issues/PRs

[shaafekhan]

Hi there. Any news on this pull request? what's the status? thank you.