update action to dagger 0.2

- Remove AGE key setup
- Update README to use `dagger do`
- Update tests to dagger 0.2

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

test/cue.mod/pkg/universe.dagger.io/go/build.cue

@@ -0,0 +1,51 @@
+package go
+
+import (
+	"dagger.io/dagger"
+)
+
+// Build a go binary
+#Build: {
+	// Source code
+	source: dagger.#FS
+
+	// Target package to build
+	package: *"." | string
+
+	// Target architecture
+	arch: *"amd64" | string
+
+	// Target OS
+	os: *"linux" | string
+
+	// Build tags to use for building
+	tags: *"" | string
+
+	// LDFLAGS to use for linking
+	ldflags: *"" | string
+
+	env: [string]: string
+
+	container: #Container & {
+		"source": source
+		"env": {
+			env
+			GOOS:   os
+			GOARCH: arch
+		}
+		command: {
+			args: [package]
+			flags: {
+				build:      true
+				"-v":       true
+				"-tags":    tags
+				"-ldflags": ldflags
+				"-o":       "/output/"
+			}
+		}
+		export: directories: "/output": _
+	}
+
+	// Directory containing the output of the build
+	output: container.export.directories."/output"
+}