DO NOT MERGE (yet) - Fix gnupg/rpm/deb containers

[chevdor]

• rename nonroot as user
• fix acl: some of the files were not owned by the nonroot user
• add gpg2 symlink (required)

From the readme:

Used as base for tooling that requires gnupg. GPG usually requires working with the gpg-agent.
Using the gpg-agent in a rootless context can be challenging as you will need to align the UID
in the container with the UIDs of your local system.

While we could make an image with UID that could be passed as ARG, this will likely always endup
being the wrong UID. For this reason, this image is creating the users at runtime.
By default, the UID is 1000 but you may customize it using the LOCAL_USER_ID environment variable.
This will allow downstream images such as paritytech/rpm and paritytech/deb to be ran with the "right"
UID and allows mapping the gpg-agent socket for the right UID.

This PR fixes the rootless rpm container calls as long as called like:

podman run  --rm -it \
   -v "/run/user/$(id -u)/gnupg/S.gpg-agent:/home/user/.gnupg/S.gpg-agent" \
   -v "$PWD/polkadot-0.9.23-1.x86_64.rpm:/home/user/polkadot-0.9.23-1.x86_64.rpm" \
   -v "$HOME/.gnupg/pubring.kbx:/home/user/.gnupg/pubring.kbx" \
    chevdor/rpm  \
   "rpm --addsign polkadot-0.9.23-1.x86_64.rpm"

[chevdor]

The RPM part can be dropped once paritytech/polkadot#6595 is merged

[chevdor]

We no longer support RPM so those changes and the rpm container could be dropped but the other chanegs may still be relevant.