[Bug] Args not resolved in multi-stage build

[gabyx]

Actual behavior
Accessing ARGs in previous stages are not resolved correctly.

Expected behavior
They should be resolved.

To Reproduce

FROM alpine:latest as base
ARG NAME="1234"
RUN echo "base:: $NAME"

FROM base AS base-dev
ARG NAME
RUN echo "dev:: $NAME"

FROM base-dev as base-custom
ARG NAME
RUN echo "custom::" $NAME

Build without specifying --build-arg="...".

Result: custom:: . ($NAME is empty) but should be 1234)

Triage Notes for the Maintainers

Description	Yes/No
Please check if this a new feature you are proposing
Please check if the build works in docker but not in kaniko
Please check if this error is seen when you use --cache flag
Please check if your dockerfile is a multistage dockerfile

[gabyx]

Related: #1160

[gabyx]

I see that here
only the Meta variables (before the first FROM) are retrieved.

Shouldn't it look also in the build args (for what stands "allowed args" ?)

} else {
		args := ba.GetAllAllowed()
		if value, ok := args[resolvedKey]; ok {
			resolvedValue = &value
		}
		meta := ba.GetAllMeta()
		if value, ok := meta[resolvedKey]; ok {
			resolvedValue = &value
		}
	}