chore: update dashboard to 0.20.0

Makefile

@@ -8,7 +8,7 @@ export EMQX_DEFAULT_BUILDER = ghcr.io/emqx/emqx-builder/5.0-5:1.13.2-24.1.5-4-al
 export EMQX_DEFAULT_RUNNER = alpine:3.14
 export OTP_VSN ?= $(shell $(CURDIR)/scripts/get-otp-vsn.sh)
 export ELIXIR_VSN ?= $(shell $(CURDIR)/scripts/get-elixir-vsn.sh)
-export EMQX_DASHBOARD_VERSION ?= v0.19.0
+export EMQX_DASHBOARD_VERSION ?= v0.20.0
 export DOCKERFILE := deploy/docker/Dockerfile
 export DOCKERFILE_TESTING := deploy/docker/Dockerfile.testing
 ifeq ($(OS),Windows_NT)