feat: add {add,remove}-copybara-credential-store roles

Change-Id: I4f054ceb410b3082b109a5c24e3e9a8105c6c169
diff --git a/roles/remove-copybara-credential-store/defaults/main.yaml b/roles/remove-copybara-credential-store/defaults/main.yaml
new file mode 100644
index 0000000..db10a19
--- /dev/null
+++ b/roles/remove-copybara-credential-store/defaults/main.yaml
@@ -0,0 +1 @@
+filename: "~/.git-credentials"