Add support for partial checkout filters (#1396)

* added filter option & tests

* added build file

* fix test oversight

* added exit 1

* updated docs to specify override

* undo unneeded readme change

* set to undefined rather than empty string

* run git config in correct di

---------

Co-authored-by: Cory Miller <13227161+cory-miller@users.noreply.github.com>

.github/workflows/test.yml

@@ -72,6 +72,16 @@ jobs:
         shell: bash
         run: __test__/verify-side-by-side.sh
 
+      # Filter
+      - name: Fetch filter
+        uses: ./
+        with:
+          filter: 'blob:none'
+          path: fetch-filter
+
+      - name: Verify fetch filter
+        run: __test__/verify-fetch-filter.sh
+
       # Sparse checkout
       - name: Sparse checkout
         uses: ./