multi-stage dockerfile: This reduces image size to half compare to ea…

[StarTrooper08]

multi-stage dockerfile: This reduces image size to half compare to earlier image version size.

Before multi-stage build

After multi-stage build(r-multi-stage build -> r-dev-env image)

[hturner]

This looks okay to me, but I see ubuntu 22.04 is hard-coded. Maybe we can use ubuntu-latest to avoid needed to update later?

[StarTrooper08]

If we use just ubuntu instead of ubuntu:22, it will automatically used as latest.
Will make the following change and also have a look over build process.