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/alpine/alpine.cue

@@ -0,0 +1,42 @@
+// Base package for Alpine Linux
+package alpine
+
+import (
+	"universe.dagger.io/docker"
+)
+
+// Build an Alpine Linux container image
+#Build: {
+
+	// Alpine version to install.
+	version: string | *"3.15.0@sha256:21a3deaa0d32a8057914f36584b5288d2e5ecc984380bc0118285c70fa8c9300"
+
+	// List of packages to install
+	packages: [pkgName=string]: {
+		// NOTE(samalba, gh issue #1532):
+		//   it's not recommended to pin the version as it is already pinned by the major Alpine version
+		//   version pinning is for future use (as soon as we support custom repositories like `community`,
+		//   `testing` or `edge`)
+		version: string | *""
+	}
+
+	docker.#Build & {
+		steps: [
+			docker.#Pull & {
+				source: "index.docker.io/alpine:\(version)"
+			},
+			for pkgName, pkg in packages {
+				docker.#Run & {
+					command: {
+						name: "apk"
+						args: ["add", "\(pkgName)\(pkg.version)"]
+						flags: {
+							"-U":         true
+							"--no-cache": true
+						}
+					}
+				}
+			},
+		]
+	}
+}

test/cue.mod/pkg/universe.dagger.io/alpine/test/test.bats

@@ -0,0 +1,8 @@
+setup() {
+    load '../../bats_helpers'
+
+    common_setup
+}
+@test "alpine" {
+    dagger up
+}

test/cue.mod/pkg/universe.dagger.io/alpine/test/test.cue

@@ -0,0 +1,52 @@
+package alpine
+
+import (
+	"dagger.io/dagger"
+
+	"universe.dagger.io/alpine"
+	"universe.dagger.io/docker"
+)
+
+dagger.#Plan & {
+	actions: tests: {
+		// Test: customize alpine version
+		alpineVersion: {
+			build: alpine.#Build & {
+				// install an old version on purpose
+				version: "3.10.9"
+			}
+
+			verify: dagger.#Readfile & {
+				input:    build.output.rootfs
+				path:     "/etc/alpine-release"
+				contents: "3.10.9\n"
+			}
+		}
+
+		// Test: install packages
+		packageInstall: {
+			build: alpine.#Build & {
+				packages: {
+					jq: {}
+					curl: {}
+				}
+			}
+
+			check: docker.#Run & {
+				input: build.output
+				command: {
+					name: "sh"
+					flags: "-c": """
+						jq --version > /jq-version.txt
+						curl --version > /curl-version.txt
+						"""
+				}
+
+				export: files: {
+					"/jq-version.txt": contents:   =~"^jq"
+					"/curl-version.txt": contents: =~"^curl"
+				}
+			}
+		}
+	}
+}