Add caddy server static PIE build

caddy/.gitignore

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+/caddy-*
+/v2.*.tar.gz

caddy/README.md

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+# Build caddy server as static PIE
+
+Build the [caddy server](https://caddyserver.com/) web server as a static PIE ELF running on Linux.
+
+## Requirements
+
+Make sure the following packages are installed:
+* go >= 1.17
+
+## Build
+
+The `caddy` static PIE ELF is located in the current folder.
+If you want to rebuild it, run:
+
+```
+$ ./build.sh
+```
+
+## Run
+
+You can run the executable natively on Linux:
+
+```
+$ ./caddy-2.6.2/cmd/caddy/caddy respond --debug --access-log --listen :8089 "Hello world\!"
+```
+
+Or with [run-elfloader](https://github.com/unikraft/run-app-elfloader) on Unikraft:
+```
+$ ./run_elfloader ../static-pie-apps/caddy/caddy-2.6.2/cmd/caddy/caddy [args]
+```
+

caddy/build.sh

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+#!/bin/sh
+
+# Clean up
+rm -rf caddy-*
+rm -f v2.*
+
+echo "Downloading caddy source code... "
+wget -q https://github.com/caddyserver/caddy/archive/refs/tags/v2.6.2.tar.gz
+
+echo "Unpacking caddy source code..."
+tar xzf v2.6.2.tar.gz
+
+echo "Building caddy... "
+cd caddy-2.6.2/cmd/caddy
+CGO_ENABLED=1 go build -buildmode=pie -ldflags "-linkmode external -extldflags "-static-pie""
+echo ""

caddy/rootfs/Caddyfile

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+:80
+
+route {
+    teapot
+}