allow user to specify cache path

.github/workflows/data.yml

@@ -9,6 +9,10 @@ on:
         type: boolean
         required: false
         default: true
+      cache_path:
+        type: string
+        required: false
+        default: ""
     outputs:
       cache_key:
         value: ${{ jobs.combine_data_cache.outputs.cache_key }}
@@ -55,7 +59,7 @@ jobs:
       - run: echo WEBBPSF_PATH=${{ runner.temp }}/data/webbpsf-data/ >> $GITHUB_ENV
       - id: cache
         run: |
-          echo path=${{ runner.temp }}/data/ >> $GITHUB_OUTPUT
+          echo path=${{ inputs.cache_path != '' && inputs.cache_path || format('{0}/data', runner.temp) }} >> $GITHUB_OUTPUT
           echo key=data-${{ needs.download_webbpsf_data.outputs.cache_key }}-galsim-data-${{ steps.galsim_data.outputs.hash }} >> $GITHUB_OUTPUT
       # save a new cache to the same generalized data directory, combined with extra data
       - name: save a single combined data cache