Introduce per-repo docs build workflow.

[jouillet]

📝 Description

Introduce per-repo docs build workflow. This allows greater control over the documentation build without needing to be tied to the orch-ci repo. NOTE: Some actions are still borrowed from orch-ci, such as configuring AWS credentials, but the documentation specific actions are now local.

✨ Type of Change

Select the type of change your PR introduces:

• 🐞 Bug fix – Non-breaking change which fixes an issue
• 🚀 New feature – Non-breaking change which adds functionality
• 🔨 Refactor – Non-breaking change which refactors the code base
• 💥 Breaking change – Changes that break existing functionality
• 📚 Documentation update
• 🔒 Security update
• 🧪 Tests
• 🚂 CI

🧪 Testing Scenarios

Describe how the changes were tested and how reviewers can test them too:

• ✅ Tested manually
• 🤖 Ran automated end-to-end tests

✅ Checklist

Before submitting the PR, ensure the following:

• 🔍 PR title is clear and descriptive
• 📝 For internal contributors: If applicable, include the JIRA ticket number (e.g., ITEP-123456) in the PR title. Do not include full URLs
• 💬 I have commented my code, especially in hard-to-understand areas
• 📄 I have made corresponding changes to the documentation
• ✅ I have added tests that prove my fix is effective or my feature works

[jouillet]

NOTE: Because this is a fork, the CI actions will fail because secrets do not exist in forked repos. We should probably re-create this PR as a branch to verify that it works!

[saratpoluri]

Duplicate PR: #505 (review)