Support varying install paths for containers.conf

[jonpspri]

Currently, the system locations for containers.conf are hardcoded to /usr/share/containers/containers.conf for the Default file and /etc/containers/containers.conf for the System override. (And ~/.config/containers/containers.conf for User overrides, but that's not really at issue in this Issue.)

As we've seen in some other Podman issues, recent versions of MacOS frown on system-level installs and modifications and package management systems like Homebrew install into some less Linux-y places like /opt/homebrew.

I propose we make the search for containers.conf more intelligent by inferring an install prefix based on the location of the binary that is currently executing. For example, if the currently executing binary is /opt/homebrew/bin/podman we can infer that InstallPrefix is /opt/homebrew. Then our search logic becomes:

Default file: ${Prefix}/share/containers/containers.conf fall back to /usr/share/containers/containers.conf System file: ${Prefix}/etc/containers/containers.conf fall back to /etc/containers/containers.conf

I welcome thoughts from other contributors before launching into a PR.

Here is the current code...

https://github.com/containers/common/blob/2d46695412078739031f92901d73e28f01200d3a/pkg/config/config.go#L21-L31

https://github.com/containers/common/blob/2d46695412078739031f92901d73e28f01200d3a/pkg/config/config.go#L600

[rhatdan]

I am fine with this change, BUT this is more then just the code. Documentation and Google Memory will make this difficult.