[Hub apps] Create the hub-event-trigger module for creating ADF triggers

[flanakin]

🛠️ Description

Creates a placeholder for the hub-event-trigger module that will eventually be used for publishing hub events based on storage and schedule events.

This PR does not introduce eventing. The intent is to get this into place so we can bring eventing in later. This should not change how anything operates. It only changes how the resources are defined. Schedule events will be added in a separate PR. This only covers storage events.

Related to #1400

📋 Checklist

🔬 How did you test this change?

• 🤏 Lint tests
• 🤞 PS -WhatIf / az validate
• 👍 Manually deployed + verified
• 💪 Unit tests
• 🙌 Integration tests

🙋‍♀️ Do any of the following that apply?

• 🚨 This is a breaking change.
• 🤏 The change is less than 20 lines of code.

📑 Did you update docs/changelog.md?

• ✅ Updated changelog (required for dev PRs)
• ➡️ Will add log in a future PR (feature branch PRs only)
• ❎ Log not needed (small/internal change)

📖 Did you update documentation?

• ✅ Public docs in docs (required for dev)
• ✅ Internal dev docs in src (required for dev)
• ➡️ Will add docs in a future PR (feature branch PRs only)
• ❎ Docs not needed (small/internal change)