Switch from stacks to targets AKA "Stay on target"

Buildpack API 0.10 removed the concept of stacks in favor of targets heroku/libcnb.rs#773. 

This commit works to upgrade applications in place by migrating metadata to support the new serialization format. This is supported by implementing TryMigrate from the `magic_migrate` crate https://docs.rs/magic_migrate/latest/magic_migrate/macro.try_migrate_link.html. 


https://www.youtube.com/watch?v=NnP5iDKwuwk

buildpacks/ruby/Cargo.toml

@@ -16,7 +16,7 @@ glob = "0.3"
 indoc = "2"
 # libcnb has a much bigger impact on buildpack behaviour than any other dependencies,
 # so it's pinned to an exact version to isolate it from lockfile refreshes.
-libcnb = "=0.19.0"
+libcnb = "=0.21.0"
 libherokubuildpack = { version = "=0.21.0", default-features = false, features = ["digest"] }
 rand = "0.8"
 # TODO: Consolidate on either the regex crate or the fancy-regex crate, since this repo currently uses both.
@@ -27,7 +27,8 @@ tempfile = "3"
 thiserror = "1"
 ureq = { version = "2", default-features = false, features = ["tls"] }
 url = "2"
+magic_migrate = "0.1"
+toml = "0.8"
 
 [dev-dependencies]
-libcnb-test = "=0.19.0"
-toml = "0.8"
+libcnb-test = "=0.21.0"

buildpacks/ruby/buildpack.toml

@@ -12,10 +12,23 @@ keywords = ["ruby", "rails", "heroku"]
 type = "BSD-3-Clause"
 
 [[stacks]]
-id = "heroku-20"
-
-[[stacks]]
-id = "heroku-22"
+id = "*"
 
 [metadata.release]
 image = { repository = "docker.io/heroku/buildpack-ruby" }
+
+[[targets]]
+os = "linux"
+arch = "arm64"
+
+[[targets]]
+os = "linux"
+arch = "amd64"
+
+[[targets.distros]]
+name = "ubuntu"
+version = "20.04"
+
+[[targets.distros]]
+name = "ubuntu"
+version = "22.04"