adds and configures a dev container for code spaces

Author: nickfloyd

.devcontainer/Docker

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+# See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.234.0/containers/dotnet/.devcontainer/base.Dockerfile
+# [Choice] .NET version: 6.0, 5.0, 3.1, 6.0-bullseye, 5.0-bullseye, 3.1-bullseye, 6.0-focal, 5.0-focal, 3.1-focal
+ARG VARIANT="6.0-bullseye"
+FROM mcr.microsoft.com/vscode/devcontainers/dotnet
+
+# "install" the dotnet 3.1 & 6.0 runtime for tests
+COPY --from=mcr.microsoft.com/dotnet/sdk:3.1 /usr/share/dotnet/shared /usr/share/dotnet/shared
+COPY --from=mcr.microsoft.com/dotnet/sdk:6.0 /usr/share/dotnet/shared /usr/share/dotnet/shared
+
+# Add mono complete for omnisharp
+RUN apt-get install -y mono-complete

.devcontainer/devcontainer.json

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+// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
+// https://github.com/microsoft/vscode-dev-containers/tree/v0.234.0/containers/dotnet
+{
+  "name": "Octokit.net",
+  "build": {
+    "dockerfile": "Dockerfile",
+    "args": {
+      // Update 'VARIANT' to pick a .NET Core version: 3.1, 5.0, 6.0
+      // Append -bullseye or -focal to pin to an OS version.
+      "VARIANT": "latest"
+    }
+  },
+  // Set *default* container specific settings.json values on container create.
+  "settings": {
+    "omnisharp.path": "latest",
+    "omnisharp.defaultLaunchSolution": "Octokit.GraphQL.sln",
+    "omnisharp.disableMSBuildDiagnosticWarning": false,
+    "omnisharp.useModernNet": true,
+    "omnisharp.enableAsyncCompletion": true,
+    "omnisharp.enableEditorConfigSupport": true,
+    "omnisharp.enableImportCompletion": true,
+    "omnisharp.enableRoslynAnalyzers": true,
+    "omnisharp.organizeImportsOnFormat": true
+  },
+  // Add the IDs of extensions you want installed when the container is created.
+  "extensions": [
+    "ms-dotnettools.csharp",
+    "eamodio.gitlens",
+    "fernandoescolar.vscode-solution-explorer",
+    "redhat.vscode-yaml"
+  ],
+  // This is needed so that the C# extension can resolve to the correct SDK version
+  "remoteEnv": {
+    "PATH": "${containerWorkspaceFolder}/.dotnet:${containerEnv:PATH}",
+    "DOTNET_MULTILEVEL_LOOKUP": "0",
+    "TARGET": "net7.0",
+    "DOTNET_WATCH_SUPPRESS_LAUNCH_BROWSER": "true"
+  }
+}