replace "dep" with "go mod"

A simple "go mod init && go mod tidy && go mod vendor" was enough and
mostly seems to have picked the same revisions of the dependencies as
before. Notable exceptions are klog and gogo/protobuf.

vendor/sigs.k8s.io/yaml/OWNERS

@@ -0,0 +1,25 @@
+approvers:
+- dims
+- lavalamp
+- smarterclayton
+- deads2k
+- sttts
+- liggitt
+- caesarxuchao
+reviewers:
+- dims
+- thockin
+- lavalamp
+- smarterclayton
+- wojtek-t
+- deads2k
+- derekwaynecarr
+- caesarxuchao
+- mikedanese
+- liggitt
+- gmarek
+- sttts
+- ncdc
+- tallclair
+labels:
+- sig/api-machinery