Add support for RHEL 8

[bthomee]

This PR adds support for RHEL 8, and makes related tweaks.

Specifically:

• RHEL 8 does not have the perl-File-Compare, perl-File-Copy and perl-FindBin packages, even though this page says they are available from version RHEL 8.1 onward, and the latest UBI 8 image we're using contains RHEL 8.10. However, I manually created and pushed a Docker image without these packages and was able to build rippled with it. Thus the necessary packages appears to be already included in the base image, or OpenSSL 3.5.4 doesn't need them anymore or just not on RHEL 8.
• RHEL 8 does not have the rpmdevtools package, and none of the RHEL images have rpm-sign that we also need. Adding them requires registering via subscription-manager, which is a nuisance. Instead we will perform the signing in the tools-rippled image for which we will create a separate PR.
• The cleanup job was still referring to the old 9.4 and 9.6, so this is now fixed.

[bthomee]

@Bronek I made some changes to the GCC combinations to build, based on offline conversations. However, @legleux is building the .rpm using rhel-9:gcc-12. And since one of the node operators is still running RHEL 8, we should probably target more or different configurations.

What's the list of configs you recommend we build for RHEL 8, 9, and 10?

[legleux]

I would strongly suggest adhering to our commitment, or abandon it.

Get it from the distro repo be it Rocky or RH... not both.

We should have the credentials, we can just login and install it.
Didn't realize this was an account tied to you.

docker run --rm -it registry.access.redhat.com/ubi8/ubi
...
[root@341a31b0de71 /]# subscription-manager register --username $u --password $pw
Registering to: subscription.rhsm.redhat.com:443/subscription
...
[root@341a31b0de71 /]# dnf list all | grep -E '(rpmdevtools|rpm-sign|gold)'
gcc-toolset-12-binutils-gold.x86_64                    2.38-17.el8                                                  rhel-8-for-x86_64-appstream-rpms 
gcc-toolset-12-binutils-gold.x86_64                    2.38-17.el8                                                  ubi-8-appstream-rpms             
gcc-toolset-13-binutils-gold.x86_64                    2.40-21.el8                                                  rhel-8-for-x86_64-appstream-rpms 
gcc-toolset-13-binutils-gold.x86_64                    2.40-21.el8                                                  ubi-8-appstream-rpms             
gcc-toolset-14-binutils-gold.x86_64                    2.41-4.el8_10                                                rhel-8-for-x86_64-appstream-rpms 
gcc-toolset-14-binutils-gold.x86_64                    2.41-4.el8_10                                                ubi-8-appstream-rpms             
rpm-sign.x86_64                                        4.14.3-32.el8_10                                             rhel-8-for-x86_64-baseos-rpms    
rpmdevtools.noarch                                     8.10-8.el8     

[bthomee]

We can ignore the cleanup failure - it will succeed once the first RHEL 8 image gets pushed.