[CI] [Test] Enforces equal or increasing code coverage in PRs (#1559) (…

…#1591)

* Utilizes Codecov yaml configuration: https://docs.codecov.com/docs/codecov-yaml
* The purpose of enforcing increasing code coverage over time is to attempt to improve the quality of
  changes via testing, reduce the need to request tests in PRs, and stay away from enforcing an
  ambiguous coverage percentage.

Signed-off-by: Tommy Markley <markleyt@amazon.com>
(cherry picked from commit 21d7b6f)

.github/.codecov.yml

@@ -0,0 +1,7 @@
+# https://docs.codecov.com/docs/codecov-yaml
+coverage:
+  status:
+    project:
+      default:
+        # https://docs.codecov.com/docs/commit-status#target
+        target: auto  # coverage must be equal or above the previous commit