add docker build chain

.dockerignore

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+*.pdb
+*.Development.json
+**bin
+**obj

.github/workflows/docker.yml

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+name: Docker
+on: push
+jobs:
+  docker:
+    name: GitHub Packages
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - id: meta
+        uses: docker/metadata-action@v4
+        with:
+          images: ghcr.io/walzen-group/BeatTogether.UnifiedServer/beat-together-unified-server
+          tags: |
+            type=ref,event=branch
+            type=ref,event=pr
+            type=semver,pattern={{version}}
+            type=semver,pattern={{major}}.{{minor}}
+            type=semver,pattern={{major}}
+            type=sha
+      - uses: docker/setup-buildx-action@v2
+      - uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - uses: docker/setup-qemu-action@v2
+      - uses: docker/build-push-action@v4
+        with:
+          push: true
+          platforms: linux/amd64
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          cache-from: type=gha
+          cache-to: type=gha,mode=max

Dockerfile

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+# Stage 1: Build the .NET application
+FROM mcr.microsoft.com/dotnet/sdk:6.0 AS build
+WORKDIR /app
+
+# Copy everything from the host machine into the container
+COPY . .
+
+RUN dotnet clean BeatTogether.UnifiedServer.sln -c Release
+
+# Build for linux x64 for now (no multiarch support yet)
+RUN dotnet publish BeatTogether.UnifiedServer.sln -p:PublishReadyToRun=true -p:PublishTrimmed=false -p:TargetFramework=net6.0 -r linux-x64 -o /tmp/out
+
+# Stage 2: Create a new runtime container
+# FROM mcr.microsoft.com/dotnet/runtime:6.0 AS runtime
+FROM mcr.microsoft.com/dotnet/runtime:6.0 AS runtime
+
+WORKDIR /app
+
+# Copy the published output from the build stage
+COPY --from=build /tmp/out /app
+
+ENTRYPOINT ["/app/BeatTogether.UnifiedServer"]