Introduce a printer interface for flux resource

If implemented, there will a common interface to print flux resource.

We are adding new way to print resource information e.g. diff of
objects.

Signed-off-by: Soule BA <soule@weave.works>

pkg/printers/interface.go

@@ -0,0 +1,33 @@
+/*
+Copyright 2022 The Flux authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package printers
+
+import "io"
+
+// Printer is an interface for printing Flux cmd	outputs.
+type Printer interface {
+	// Print prints the given args to the given writer.
+	Print(io.Writer, ...interface{}) error
+}
+
+// PrinterFunc is a function that can print args to a writer.
+type PrinterFunc func(w io.Writer, args ...interface{}) error
+
+// Print implements Printer
+func (fn PrinterFunc) Print(w io.Writer, args ...interface{}) error {
+	return fn(w, args)
+}