Add --format to docker service ps

This fix tries to address the issue raised in 27189 where
it is not possible to support configured formatting stored in
config.json.

Since `--format` was not supported in `docker service ps`,
the flag `--format` has also been added in this fix.

This fix
1. Add `--format` to `docker service ps`
2. Add `tasksFormat` to config.json
3. Add `--format` to `docker stack ps`
4. Add `--format` to `docker node ps`

The related docs has been updated.

An integration test has been added.

This fix fixes 27189.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

config/configfile/file.go

@@ -36,6 +36,7 @@ type ConfigFile struct {
 	Filename             string                      `json:"-"` // Note: for internal use only
 	ServiceInspectFormat string                      `json:"serviceInspectFormat,omitempty"`
 	ServicesFormat       string                      `json:"servicesFormat,omitempty"`
+	TasksFormat          string                      `json:"tasksFormat,omitempty"`
 }
 
 // LegacyLoadFromReader reads the non-nested configuration data given and sets up the