feat: add --format json support to plugin:list

Adds a `--format json` flag to `plugin:list` whose output includes each plugin's install source - for git-based third-party plugins, the git remote URL, the checked-out commit, and the followed branch - so the set of installed plugins can be reconstructed elsewhere.

Closes #8798.

plugins/plugin/src/plugin-list/plugin-list.go

@@ -0,0 +1,20 @@
+package main
+
+import (
+	"os"
+
+	"github.com/dokku/dokku/plugins/common"
+	"github.com/dokku/dokku/plugins/plugin"
+
+	flag "github.com/spf13/pflag"
+)
+
+func main() {
+	args := flag.NewFlagSet("plugin:list", flag.ExitOnError)
+	format := args.String("format", "json", "format: [ json ]")
+	args.Parse(os.Args[1:])
+
+	if err := plugin.CommandList(*format); err != nil {
+		common.LogFailWithError(err)
+	}
+}