chore: Remove the Makefile backup target (#3000)

* chore: Remove `backup` target from Makefile

- The `backup` target is no longer serving any value to us. It was made redundant with changes added in Oct 2020.
- `clean` target inline docs revised.
- `.gitignore` remove test lines that are no longer valid.

* chore: Parallel test target split to multi-line

* tests(fix): Test `setup.sh` with temporary config dir

The `no_containers.bats` test has many redundant test cases already covered by `setup-cli`. They're basically identical. Removed all but one.

This removes some config dirs that were being explicitly created instead of using the test helper to generate a directory that can be used to test the `-p` option instead.

* ci: Ensure tests are run when `Makefile` is modified

.github/workflows/test_merge_requests.yml

@@ -1,4 +1,4 @@
-name: 'Test Merge Requests'
+name: "Test Merge Requests"
 
 on:
   workflow_dispatch:
@@ -9,6 +9,7 @@ on:
       - .dockerignore
       - .gitmodules
       - Dockerfile
+      - Makefile
       - setup.sh
 
 permissions:
@@ -16,18 +17,18 @@ permissions:
 
 jobs:
   build-image-amd64:
-    name: 'Build AMD64 Image'
+    name: "Build AMD64 Image"
     uses: docker-mailserver/docker-mailserver/.github/workflows/generic_build.yml@master
 
   run-tests:
-    name: 'Test AMD64 Image'
+    name: "Test AMD64 Image"
     needs: build-image-amd64
     uses: docker-mailserver/docker-mailserver/.github/workflows/generic_test.yml@master
     with:
       cache-key: ${{ needs.build-image-amd64.outputs.build-cache-key }}
 
   job-build-arm:
-    name: 'Build ARM64 Image'
+    name: "Build ARM64 Image"
     # Dependency ensures the cache-key is only created for AMD64 builds.
     # ARM64 will not be able to use this cache, building from scratch each time.
     # Expect about 2 minutes extra build time until adopting `type=gha` with scopes for cache.