refactor: migrate docker-options subcommands to go

Ports the user-facing CLI subcommands and lifecycle triggers from bash to go, mirroring the layout used by the ports plugin. The on-disk format (`DOCKER_OPTIONS_BUILD/DEPLOY/RUN` files), the `docker-args-build/deploy/run` triggers, and every exported helper consumed by other plugins are unchanged. Reserves the `--process` and `--global` flags on add, remove, and clear so usage today exits with a not-yet-implemented error and the surface is locked in ahead of the process-scoping work tracked in #2441.

plugins/docker-options/internal-functions.go

@@ -0,0 +1,45 @@
+package dockeroptions
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
+
+var availablePhases = []string{"build", "deploy", "run"}
+
+func parsePhases(phasesArg string) ([]string, error) {
+	if phasesArg == "" {
+		return nil, nil
+	}
+
+	phases := strings.Split(phasesArg, ",")
+	for _, phase := range phases {
+		valid := false
+		for _, allowed := range availablePhases {
+			if phase == allowed {
+				valid = true
+				break
+			}
+		}
+		if !valid {
+			return nil, fmt.Errorf("Phase(s) must be one of [%s]", strings.Join(availablePhases, " "))
+		}
+	}
+
+	return phases, nil
+}
+
+// ErrIfReservedFlagsUsed returns a not-yet-implemented error when --process or --global are passed.
+// Both flags are reserved for the upcoming process-scoped docker options work (issue #2441).
+func ErrIfReservedFlagsUsed(processes []string, global bool) error {
+	if len(processes) == 0 && !global {
+		return nil
+	}
+
+	if len(processes) > 0 && global {
+		return errors.New("--process and --global flags are mutually exclusive")
+	}
+
+	return errors.New("--process and --global flags are reserved for a future release and not yet implemented")
+}