feat: migrate builds plugin to go and track per-build records

Adds typed JSON build records under data/builds/<app>/<build-id>.{json,log} keyed on a stable base36 ULID-style DOKKU_BUILD_ID generated for every deploy. The new commands surface that history (builds:list, builds:info, builds:prune) and an operator-configurable retention via builds:set retention. The existing builds:cancel and builds:output now key on the build-id (with safe handling for already-finalized and abandoned records), and the per-build log file replaces journalctl as the durable source of truth for builds:output.

plugins/builds/set.go

@@ -0,0 +1,44 @@
+package builds
+
+import (
+	"fmt"
+	"strconv"
+
+	"github.com/dokku/dokku/plugins/common"
+)
+
+// CommandSet writes (or clears) a builds property for an app or globally.
+func CommandSet(appName, property, value string) error {
+	if appName != "--global" {
+		if err := common.VerifyAppName(appName); err != nil {
+			return err
+		}
+	}
+
+	if _, ok := DefaultProperties[property]; !ok {
+		return fmt.Errorf("Invalid property %q (allowed: retention)", property)
+	}
+
+	if value != "" {
+		if err := validateSetValue(property, value); err != nil {
+			return err
+		}
+	}
+
+	common.CommandPropertySet("builds", appName, property, value, DefaultProperties, GlobalProperties)
+	return nil
+}
+
+func validateSetValue(property, value string) error {
+	switch property {
+	case "retention":
+		n, err := strconv.Atoi(value)
+		if err != nil {
+			return fmt.Errorf("Invalid retention %q: must be a positive integer", value)
+		}
+		if n < MinimumRetention {
+			return fmt.Errorf("Invalid retention %d: must be >= %d", n, MinimumRetention)
+		}
+	}
+	return nil
+}