feat: add configurable cache key with template variable support (#246)

I closed [this PR](https://github.com/jdx/mise-action/pull/235) by
mistake so I'm reopening it.

.github/workflows/test.yml

@@ -105,6 +105,23 @@ jobs:
           exit 1
         if: ${{ steps.bad.outcome != 'failure' }}
 
+  custom_cache_key:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4
+      - name: Setup mise with custom cache key
+        uses: ./
+        with:
+          cache_key: "custom-{{platform}}-{{install_args_hash}}-${{ github.run_id }}"
+          install_args: "jq@1.7.1"
+          mise_toml: |
+            [tools]
+            jq = "1.7.1"
+      - run: mise --version
+      - run: mise x jq -- jq --version
+      - run: which jq
+      - run: jq --version
+
   fetch_from_github:
     runs-on: ubuntu-latest
     steps: