[CentOS] CentOS Stream 8 EOL

As announced multiple times (see https://blog.centos.org/2023/04/end-dates-are-coming-for-centos-stream-8-and...) , CentOS Stream 8 reached now EOL (End Of Life)

That means that all content was removed from http://mirror.centos.org/centos/8-stream/ (and so from downstream third-party mirrors) earlier today.

The latest compose from today was archived to Vault (https://vault.centos.org/8-stream/) and will *never* receive any more update (security or else)

SIGs content was also archived to same place, and koji/buildsystem tags "locked down".

To reflect that "unmaintained state", mirrorlist.centos.org started also to answer "Invalid release/repo/arch combination" , like we always did for all the previous EOL'ed releases.