Set the cache-dependency-glob default to **/uv.lock (#77)

We should aim for a solution with sane defaults that work as most users
would expect it.

The current default leads to a cache that is never invalidated and thus
never updated.

This also mirrors the default behaviors for setup-python which use
`**/requirements.txt`, `**/Pipfile.lock` or `**/poetry.lock`

Also make it clear that the uv cache on the filesystem can be uploaded to the GitHub Actions cache, but they are distinct things.

Also make it clear that the local cache path can be changed without using `enable-cache: true`

action.yml

@@ -20,8 +20,8 @@ inputs:
   cache-dependency-glob:
     description:
       'Glob pattern to match files relative to the repository root to control
-      the cache. e.g. "uv.lock"'
-    required: false
+      the cache.'
+    default: "**/uv.lock"
   cache-suffix:
     description: "Suffix for the cache key"
     required: false