feat: add CHANGELOG/README/Tests to github_oidc

[jhatler]

This adds a test case to the github_oidc module to ensure that it works prior to releasing new versions. It also makes the following changes:

• Cleans up the rest of the hello_world module (#307)
• Updates the tfsec and dependabot configs (#300)
• Add CHANGELOG.md to github_oidc module (empty)
• Add README.md to github_oidc module (usage + references)

Fixes: #293, #307 Refs: #300

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