Integrate CodeCov as change acceptance stage

As a rough measure to keep quality up we want to integrate our code
coverage tooling to the point where it is required for changes to be
merged.

Example taken from https://github.com/cosmos/voyager/blob/develop/codecov.yaml

.codecov.yml

@@ -1,26 +0,0 @@
-
-#
-# This codecov.yml is the default configuration for
-# all repositories on Codecov. You may adjust the settings
-# below in your own codecov.yml in your repository.
-#
-coverage:
-  precision: 2
-  round: down
-  range: 70...100
-
-  status:
-    # Learn more at https://codecov.io/docs#yaml_default_commit_status
-    project: 
-      default:
-        threshold: 1% # allow this much decrease on project
-    changes: false
-
-comment:
-  layout: "header, diff"
-  behavior: default  # update if exists else create new
-
-ignore:
-  - "docs"
-  - "*.md"
-  - "*.rst"

codecov.yml

@@ -0,0 +1,16 @@
+coverage:
+  precision: 2
+  round: down
+  range: "70...100"
+
+  status:
+    project: on
+    patch: on
+    changes: off
+
+comment:
+  layout: "diff, files"
+  behavior: default
+  require_changes: no
+  require_base: no
+  require_head: yes