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/.gitignore

@@ -0,0 +1,20 @@
+# OSX leaves these everywhere on SMB shares
+._*
+
+# Eclipse files
+.classpath
+.project
+.settings/**
+
+# Emacs save files
+*~
+
+# Vim-related files
+[._]*.s[a-w][a-z]
+[._]s[a-w][a-z]
+*.un~
+Session.vim
+.netrwhist
+
+# Go test binaries
+*.test