ci: Run End-to-End Tests for Debug and Release Configurations

Motivation
----------

It looks like building images with containertool on Linux fails downloading the
base image `swift:slim` from dockerhub.

Modifications
-------------

Update end to end and integration workflows to test both `scratch` and `swift:slim`
base images.

Result
------

End-to-End Tests will now fail in release configuration.

Test Plan
---------

Other tests are not affected by this.

Author: herzi

.github/workflows/endtoend_tests.yml

@@ -21,6 +21,9 @@ jobs:
                     - 5000:5000
         strategy:
             matrix:
+                from:
+                    - scratch
+                    - swift:slim
                 example:
                     - Examples/HelloWorldVapor
                     - Examples/HelloWorldHummingbird
@@ -52,7 +55,7 @@ jobs:
                       --allow-network-connections all \
                       build-container-image \
                       --repository localhost:5000/example \
-                      --from scratch
+                      --from ${{ matrix.from }}
 
             - name: Run the example
               run: |