feat: implement initial version of p2p relay server (#1)

* feat: implement initial version of p2p relay server

* ci: implement github action to build and release binaries for all platforms

Author: fbozic

.github/workflows/release.yml

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+name: Build and release
+on:
+  push:
+    branches:
+      - master
+permissions: write-all
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    outputs:
+      version: ${{ steps.get_version.outputs.version }}
+      release_exists: ${{ steps.check_release.outputs.exists }}
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup rust toolchain
+        run: rustup toolchain install stable --profile minimal
+
+      - name: Setup rust cache
+        uses: Swatinem/rust-cache@v2
+
+      - name: Install cross
+        run: cargo install cross --version 0.2.5
+
+      - name: Build for Intel Linux
+        run: cargo build --release --target=x86_64-unknown-linux-gnu
+
+      - name: Build for ARM Linux
+        run: cross build --release --target=armv7-unknown-linux-gnueabihf
+
+      - name: Create artifacts directory
+        run: |
+          mkdir -p artifacts
+          cp target/x86_64-unknown-linux-gnu/release/relay-server artifacts/relay-server-x86_64-unknown-linux
+          cp target/armv7-unknown-linux-gnueabihf/release/relay-server artifacts/relay-server-armv7-unknown-linux
+
+      - name: Upload job artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: artifacts
+          path: artifacts/
+
+      - name: Get version
+        id: get_version
+        run: echo "version=$(cargo read-manifest | jq -r '.version')" >> $GITHUB_OUTPUT
+
+      - name: Check if release exists
+        id: check_release
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          RELEASE_URL=$(curl --silent "https://api.github.com/repos/calimero-network/relay-server/releases/tags/${{ steps.get_version.outputs.version }}" \
+            -H "Authorization: Bearer ${{ secrets.GITHUB_TOKEN }}" \
+            -H "Accept: application/vnd.github.v3+json" | jq -r '.url')
+          if [[ "$RELEASE_URL" != "null" ]]; then
+            echo "exists=true" >> $GITHUB_OUTPUT
+          else
+            echo "exists=false" >> $GITHUB_OUTPUT
+          fi
+
+  release:
+    name: Release
+    runs-on: ubuntu-latest
+    needs: build
+    if: needs.build.outputs.release_exists == 'false'
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Download job artifacts
+        uses: actions/download-artifact@v4
+
+      - name: Create GitHub Release
+        uses: softprops/action-gh-release@v2
+        with:
+          tag_name: ${{ needs.build.outputs.version }}
+          files: |
+            README.md
+            artifacts/*
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.gitignore

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+.idea/
+res/
+data/
+target/
+.DS_Store
+.vscode/
+
+private.key