BREAKING CHANGE: update internal modules to latest, replace github_organization with github_owner, bump Terraform version to >=0.13.1

[bryantbiggs]

Description

• add data source for using correct partition based on where Atlantis is provisioned for the default ECS task execution policy ARN
• update sub-modules to use latest versions; GitHub version need to be updated for deprecating changes
• bump min Terraform version to 0.13.1+ due to module and provider support
• replace github_organization with github_owner due to deprecation in the GitHub provider
• switch policy ARN attachment from count to for_each
• correct github-complete example project so it works correctly again (trusted principals and trusted entities)

Motivation and Context

Closes #190
Closes #192
Closes #201

Breaking Changes

• Yes; support for Terraform v0.12.x is dropped, and GitHub provider min version supported raised to v4.8.x for deprecation of github_organization

How Has This Been Tested?

• I have tested and validated these changes using one or more of the provided examples/* projects
  • complete example updated and validated with test projects
  • also fixed/updated GitHub webhook example project

[antonbabenko]

I know the PR is not ready but trusted_principals and trusted_entities are rather handy to have. Good night :)

[antonbabenko]

Thanks, @bryantbiggs !

https://github.com/terraform-aws-modules/terraform-aws-atlantis/releases/tag/v3.0.0

[github-actions]

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