MDBF-1156: Add Ubuntu 26.04v3 builder - migration release add galera

[grooverdan]

obvious #924 dependency

[RazvanLiviuVarzaru]

Same comment as in #924 (comment)
I am thinking to change a bit the way of working as in:

• instead of the builder relying on the built-in in-container Galera, to download and install Galera instead.

In practice:

• the builder will install galera from the environment's CI. i.e. if we run it in DEV, to install galera at runtime from ci.dev.mariadb
• if we run it in production, install it on the go from ci.mariadb.org
• if galera is not yet built in the environment's CI, then Skip galera tests

The above requires a bit of re-work from my side but I think is better to handle galera installation at runtime.