chore: add lint step

In this step we check:

1. format
2. credo
3. dialyzer

.drone.yml

@@ -40,7 +40,13 @@ steps:
       POSTGRES_PASS: postgres
     commands:
       - mix do local.rebar --force, local.hex --force, deps.get, deps.compile
-      - mix test --cover --trace --slowest 10
+      - make test
+
+  - name: lint
+    image: 'elixir:1.13.4'
+    commands:
+      - mix do local.rebar --force, local.hex --force, deps.get, deps.compile
+      - make static_code_analysis
 
   - name: rebuild cache
     image: 'meltwater/drone-cache:v1.3.0'