feat: implement builder plugin

This plugin will allow users to override the builder used for their application, enabling users to use custom builders if desired.

plugins/builder/report.go

@@ -0,0 +1,44 @@
+package builder
+
+import (
+	"github.com/dokku/dokku/plugins/common"
+)
+
+// ReportSingleApp is an internal function that displays the builder report for one or more apps
+func ReportSingleApp(appName string, format string, infoFlag string) error {
+	if err := common.VerifyAppName(appName); err != nil {
+		return err
+	}
+
+	flags := map[string]common.ReportFunc{
+		"--builder-computed-selected": reportComputedSelected,
+		"--builder-global-selected":   reportGlobalSelected,
+		"--builder-selected":          reportSelected,
+	}
+
+	flagKeys := []string{}
+	for flagKey := range flags {
+		flagKeys = append(flagKeys, flagKey)
+	}
+
+	trimPrefix := false
+	uppercaseFirstCharacter := true
+	infoFlags := common.CollectReport(appName, infoFlag, flags)
+	return common.ReportSingleApp("builder", appName, infoFlag, infoFlags, flagKeys, format, trimPrefix, uppercaseFirstCharacter)
+}
+
+func reportComputedSelected(appName string) string {
+	value := reportSelected(appName)
+	if value == "" {
+		value = reportGlobalSelected(appName)
+	}
+
+	return value
+}
+func reportGlobalSelected(appName string) string {
+	return common.PropertyGet("builder", "--global", "selected")
+}
+
+func reportSelected(appName string) string {
+	return common.PropertyGet("builder", appName, "selected")
+}