feat(pod): add switch to enable checksum annotation

Depending on the environment or tooling in which the chart is deployed, you may
or may not want to have the checksum annotation.

In the past, these were enforced. The default remains that the checksum
annotation is added. It now only contains a switch that allows you to optionally
disable it.

unittests/deployment/env.yaml

@@ -35,10 +35,10 @@ tests:
             name: athens-proxy-unittest-env
       template: templates/deployment.yaml
 
-- it: Rendering default with mounted env secret
+- it: Rendering default with mounted env secret, but without sha sum annotation
   set:
     config.env.enabled: true
-    config.env.existingSecret.enabled: true
+    config.env.addSHASumAnnotation: false
   asserts:
     - notExists:
         path: spec.template.metadata.annotations.checksum/secret-athens-proxy-unittest-env
@@ -48,4 +48,37 @@ tests:
         content:
           secretRef:
             name: athens-proxy-unittest-env
+      template: templates/deployment.yaml
+
+- it: Rendering default with mounted existing env secret
+  set:
+    config.env.enabled: true
+    config.env.existingSecret.enabled: true
+    config.env.existingSecret.secretName: my-secret
+  asserts:
+    - exists:
+        path: spec.template.metadata.annotations.checksum/secret-my-secret
+      template: templates/deployment.yaml
+    - contains:
+        path: spec.template.spec.containers[0].envFrom
+        content:
+          secretRef:
+            name: my-secret
+      template: templates/deployment.yaml
+
+- it: Rendering default with mounted existing env secret, but without sha sum annotation
+  set:
+    config.env.enabled: true
+    config.env.addSHASumAnnotation: false
+    config.env.existingSecret.enabled: true
+    config.env.existingSecret.secretName: my-secret
+  asserts:
+    - notExists:
+        path: spec.template.metadata.annotations.checksum/secret-my-secret
+      template: templates/deployment.yaml
+    - contains:
+        path: spec.template.spec.containers[0].envFrom
+        content:
+          secretRef:
+            name: my-secret
       template: templates/deployment.yaml