Add new Client API

Signed-off-by: Helder Correia <174525+helderco@users.noreply.github.com>

tests/plan/client/filesystem/read/file/test.cue

@@ -0,0 +1,44 @@
+package main
+
+import (
+	"dagger.io/dagger"
+)
+
+dagger.#Plan & {
+	client: filesystem: {
+		"cmd.sh": read: contents:     "env"
+		"test.txt": read: contents:   string
+		"secret.txt": read: contents: dagger.#Secret
+	}
+	actions: {
+		image: dagger.#Pull & {
+			source: "alpine:3.15.0@sha256:e7d88de73db3d3fd9b2d63aa7f447a10fd0220b7cbf39803c803f2af9ba256b3"
+		}
+		test: {
+			concrete: dagger.#Exec & {
+				input: image.output
+				args: ["sh", "-c", client.filesystem."cmd.sh".read.contents]
+			}
+			usage: {
+				string: dagger.#Exec & {
+					input: image.output
+					args: ["test", client.filesystem."test.txt".read.contents, "=", "foo"]
+				}
+				secret: dagger.#Exec & {
+					input: image.output
+					mounts: secret: {
+						dest:     "/run/secrets/test"
+						contents: client.filesystem."secret.txt".read.contents
+					}
+					args: [
+						"sh", "-c",
+						#"""
+						test "$(cat /run/secrets/test)" = "bar"
+						ls -l /run/secrets/test | grep -- "-r--------"
+						"""#,
+					]
+				}
+			}
+		}
+	}
+}