Fixes #24986: Enable scala 3 cross compilation

[fanf]

https://issues.rudder.io/issues/24986

Merge back commits from https://github.com/Normation/rudder/pull/5701.

The main changes are:

• switching to scala 2.13.14 to have the new target,
• using -Xsource:3-cross as source argument for scalac in place of -Xsource:3

The only one missing are:

• commit:4094fbf which actually switch to scala 3
• commit:4422086 because the warning are only present with scala 3

The commits with "fixme" were reviewed like that:

• xml pattern matching: the change was mostly ok, change some selectors
• disable specs2 tests: tests were rewritten in zio-tests

Now, we need to check that everything still works in plugins

[VinceMacBuche]

needs rebase, but lgtm

[clarktsiory]

Superseded by https://github.com/Normation/rudder/pull/6421