Add SUID bit check and auto-fix for newuidmap and newgidmap in setup script

[fkerem]

This PR enhances the setup.sh script by checking for the required SUID bits on /usr/bin/newuidmap and /usr/bin/newgidmap. These permissions are necessary for rootless Podman containers to function properly when using user namespaces.

Rootless Podman requires the newuidmap and newgidmap binaries to have the SetUID bit enabled so that unprivileged users can map UID/GID ranges during container startup.

Without this, SPRING services relying on rootless containers may fail silently or exhibit permission-related issues.

Changelog:

• Checks whether both binaries have the correct SUID bit using [ -u FILE ].
• If not set:
  • Prompts the user to fix the issue with sudo chmod u+s.
  • Exits if the user declines, ensuring misconfigured environments don’t proceed.

[fkerem]

In Digital Ocean's Fedora 41, this doesn't work. This was the solution instead:

sudo chmod u-s /usr/bin/new[gu]idmap
sudo setcap cap_setuid+eip /usr/bin/newuidmap
sudo setcap cap_setgid+eip /usr/bin/newgidmap

I'll create a PR to update the readme.

[fkerem]

This can now be merged as well. An alternative solution for Fedora 41+ is documented in the Troubleshooting section of README.md as part of PR #4 .