Enhance CI workflow with versioning and packaging

Added steps to setup GitVersion, create NuGet package, and publish it along with a GitHub release.

.github/workflows/push_main.yml

@@ -0,0 +1,68 @@
+name: Build NuGet package on main branch pull request
+
+on:
+  pull_request:
+    branches:
+      - "main"
+    paths:
+      - "TimetableDesigner.Backend.Events**"
+
+jobs:
+  build:
+    name: Build and pack
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6.0.2
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v3
+        with:
+          dotnet-version: 10.0.x
+      - name: Build
+        run: dotnet build
+      - name: Setup GitVersion
+        uses: gittools/actions/gitversion/setup@v0.9.7
+        with:
+          versionSpec: 5.x
+      - name: Determine version
+        uses: gittools/actions/gitversion/execute@v0.9.7
+        id: gitversion
+        with:
+          useConfigFile: true
+          configFilePath: ./.github/config/gitversion.yml
+      - name: Create NuGet package
+        run: dotnet pack -c Release -p:Version=${{steps.gitversion.outputs.SemVer}} -p:PackageVersion=${{steps.gitversion.outputs.SemVer}} --output ${{ github.workspace}}/nuget
+      - name: Upload artifact
+        uses: actions/upload-artifact@v3
+        with:
+          name: nuget
+          path: ${{ github.workspace}}/nuget/*.nupkg
+    outputs:
+      version: ${{ steps.gitversion.outputs.SemVer }}
+  publish:
+    name: Publish 
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+      - name: Download artifact
+        uses: actions/download-artifact@v3
+        with:
+          name: nuget
+          path: ${{ github.workspace}}/nuget
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v3
+        with:
+          dotnet-version: 10.0.x
+      - name: Publish
+        run: dotnet nuget push ${{ github.workspace}}/nuget/*.nupkg --source "github" --api-key ${{ secrets.GITHUB_TOKEN }} --skip-duplicate
+      - name: Create Release
+        uses: actions/create-release@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          tag_name: ${{needs.build.outputs.version}}
+          release_name: ${{needs.build.outputs.version}}
+          draft: false
+          prerelease: false
+        
+