Update GitHub templates (#7270)

These templates are loosely based off AspNetCore's: https://github.com/aspnet/AspNetCore/tree/master/.github

Part of #7236

Author: loic-sharma

.github/ISSUE_TEMPLATE.md

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+---
+name: Bug report
+about: Report issues when hosting the NuGet Gallery
+---
+
+### For issues regarding the NuGet client tools (the Visual Studio extension, NuGet.exe command line tool, etc.), file a bug on [NuGet Home](https://github.com/nuget/home/issues).
+
+### Describe the bug
+A clear and concise description of what the bug is.
+
+### To Reproduce
+Steps to reproduce the behavior:
+1. Using this git commit of NuGetGallery '...'
+2. Run this code '....'
+3. See error
+
+### Expected behavior
+A clear and concise description of what you expected to happen.
+
+### Screenshots
+If applicable, add screenshots to help explain your problem.
+
+### Additional context
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Feature request
+about: Suggest an idea for this project
+---
+
+### Is your feature request related to a problem? Please describe.
+A clear and concise description of what the problem is.
+Example: I am trying to do [...] but [...]
+
+### Describe the solution you'd like
+A clear and concise description of what you want to happen. Include any alternative solutions you've considered.
+
+### Additional context
+Add any other context or screenshots about the feature request here.

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: NuGet.org issue
+about: Report issues on NuGet.org
+---
+
+### For issues regarding the NuGet client tools (the Visual Studio extension, NuGet.exe command line tool, etc.), file a bug on [NuGet Home](https://github.com/nuget/home/issues).
+
+### For issues connecting to NuGet.org, please refer to [this guide](https://docs.microsoft.com/en-us/nuget/faqs/nuget-faq#nugetorg-not-accessible).
+
+### For issues regarding your NuGet.org account, please refer to [this guide](https://docs.microsoft.com/en-us/nuget/faqs/nuget-faq#nugetorg-account-management).
+
+### Describe the bug
+A clear and concise description of what the bug is.
+
+### To Reproduce
+Steps to reproduce the behavior:
+1. On this URL '...'
+2. Perform this operation '...'
+3. See error
+
+### Expected behavior
+A clear and concise description of what you expected to happen.
+
+### Screenshots
+If applicable, add screenshots to help explain your problem.
+
+### Additional context
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/nugetorg_issue.md

@@ -0,0 +1,6 @@
+Summary of the changes (in less than 80 characters):
+
+* Detail 1
+* Detail 2
+
+Addresses https://github.com/NuGet/NuGetGallery/issues/123