Add Alpine 3.21 (#314)

* Upgrade Alpine 3.21

* Upgrade Alpine 3.21

* Alpine upgrade 3.21 version bump

Author: Kaniska244

src/alpine/README.md

@@ -7,7 +7,7 @@ Simple Alpine container with Git installed.
 
 | Options Id | Description | Type | Default Value |
 |-----|-----|-----|-----|
-| imageVariant | Alpine version: | string | 3.20 |
+| imageVariant | Alpine version: | string | 3.21 |
 
 This template references an image that was [pre-built](https://containers.dev/implementors/reference/#prebuilding) to automatically include needed devcontainer.json metadata.
 

src/alpine/devcontainer-template.json

@@ -1,6 +1,6 @@
 {
     "id": "alpine",
-    "version": "3.3.0",
+    "version": "3.4.0",
     "name": "Alpine",
     "description": "Simple Alpine container with Git installed.",
     "documentationURL": "https://github.com/devcontainers/templates/tree/main/src/alpine",
@@ -11,6 +11,7 @@
             "type": "string",
             "description": "Alpine version:",
             "proposals": [
+                "3.21",
                 "3.20",
                 "3.19",
                 "3.18"