Add issue templates

In order to prompt issue reporters to provide more information up front, introduce some issue templates.

This is the start of a wider initiative to add some structure to how we respond to issues.

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Thanks for the report!
+title: "[BUG]"
+labels: bug
+assignees: cillian64, tdewey-rpi
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Include steps to allow us to reproduce the error. Include your host OS,
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**Desktop (please complete the following information):**
+ - OS: [e.g. macOS 14, Windows 11, Ubuntu Server 22.04]
+
+**The name of the OS you are trying to write**
+
+**Are you using OS Customisation?**
+
+**Additional context**
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: Feature request
+about: What would you like to see from rpi-imager?
+title: "[FEATURE]"
+labels: enhancement
+assignees: cillian64, tdewey-rpi
+
+---
+
+**Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**Describe the solution you'd like**
+A clear and concise description of what you want to happen.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.