create rolling deb/rpm repositories

Before upcoming release let's create the new repository structure.

In addition to what there is now, there should be a new "11.rolling" repo (e.g. http://yum.mariadb.org/yum/11.rolling) currently with 11.3.2 release. And "11.rc" repo with 11.3.1 and 11.4.1.

After the upcoming Q2 release, 11.4.2 will be both in the 11.4/ and in the 11.rolling/
While 11.5.1 will be only in 11.rc/ there will be no 11.5/ repo.
And later 11.5.2 — only in 11.rolling/

There will be a separate task for changing the repo configurator.