Add option to yamlfmt to ignore vendor directories (#2286)

The `make fmt` target now includes YAML formatting. This is causing
an issue downstream where vendored YAML files are being formatted.
This fix excludes vendor directories (and other files) based on the
project's .gitignore.

Signed-off-by: Todd Short <tshort@redhat.com>

Author: tmshort

Makefile

@@ -188,7 +188,7 @@ fix-lint: $(GOLANGCI_LINT) #EXHELP Fix lint issues
 .PHONY: fmt
 fmt: $(YAMLFMT) #EXHELP Formats code
 	go fmt ./...
-	$(YAMLFMT) testdata
+	$(YAMLFMT) -gitignore_excludes testdata
 
 .PHONY: update-tls-profiles
 update-tls-profiles: $(GOJQ) #EXHELP Update TLS profiles from the Mozilla wiki