Add Docker images for openSUSE releases

[serock]

Add Docker images for the latest openSUSE Leap and openSUSE Tumbleweed releases. This pull request was created in response to a comment from @mosteo.

The images include the GNAT compiler from the gcc-ada package in the openSUSE repositories. Because GPRbuild is not available in the openSUSE repositories, GPRbuild is installed via alr. The images also include the latest compilers.xml from AdaCore's GPRCONFIG KB so that GPRbuild can find the runtimes that are installed under /usr/lib64/gcc/x86_64-suse-linux/$(gcc -dumpversion)/adalib rather than /usr/lib/gcc/x86_64-suse-linux/$(gcc -dumpfullversion)/adalib.

[mosteo]

Thanks for the PR, @serock . Though, I see the GNAT version in openSUSE is quite old (7.x), and I'm afraid it won't be able to compile Alire as-is.

[serock]

Thanks @mosteo. There are newer versions of GNAT available (8.2.1, 9.3.1, 10.4.0, and 11.3.0) as shown by zypper search --details gcc*-ada. If the goal is to build Alire, I could update the image to install gcc11-ada instead of gcc-ada and add any necessary symbolic links (e.g., gnatmake -> gnatmake-11). If not, I may look into getting gprbuild into the SUSE repos.

[mosteo]

The thing is, if we want to test the standard Ada ecosystem an openSUSE user is going to find, I guess we should use the default gnat. But, if that one is too old, we cannot hold back alire and contributed crates because of that.

I guess we could say that on openSUSE, if one wants to use a system gcc, it should be the latest one. Not sure what implications that could have on the rest of system packages.

Gprbuild is not an issue here, I think.