[deckhouse-cli] Preserve object-level default map

[Glitchy-Sheep]

Problem

Object schemas with both properties and a default: {...} map silently dropped the default. synthesizeValue short-circuited on isObject(s) and returned the walk output, so rule 5 (default) never fired for object nodes.

Fix

In the object branch, overlay a map-typed s.Default on top of the walked properties via deepMergeOverride. Same precedence as x-example: walked properties form the baseline, the default wins on conflicts, nested unset fields keep their synthesized fallbacks.

Before / After

Schema:

type: object
properties:
  name: { type: string }
  port: { type: integer }
default:
  name: "override"
  extra: "kept"

Before:

name: "aB3xK9pQ"   # synthesized, default ignored
port: 123

After:

name: "override"   # from default
port: 123          # from walk
extra: "kept"      # from default