distro/rhel85: automatically convert to LVM on fs customizations

Whenever we create a new mountpoint due to a user customization,
ensure the layout uses LVM, i.e. convert plain layouts to it, if
needed. This does not apply to rpm-ostree based systems.
Add "lvm2" to the build pipeline and thus generate new manifests
and image infos.
Adjust the existing tests that assumed we can not create more
than 4 partitions on mbr layouts, since that is now not true
anymore.
This is a port from rhel86, commit 63aa155

The change in osPipeline() is required now to fix the Prefix for the
bootloader specification when LVM is used. The unspecified Prefix, which
was previously used for all cases, defaults to "/boot". When the layout
is converted to LVM, a boot partition is created and the BLS Prefix
should be set to "".

In the case where we don't have a partition table, the BLS stage is not
needed, but it was done unconditionally before, so keep the default
image definitions unchanged.

Co-Authored-By: Achilleas Koutsou <achilleas@koutsou.net>

tools/test-case-generators/distro-arch-imagetype-map.json

@@ -134,6 +134,7 @@
             "qcow2",
             "edge-commit",
             "edge-container",
+            "edge-installer",
             "image-installer",
             "vhd",
             "vmdk"
@@ -145,6 +146,7 @@
             "qcow2",
             "edge-commit",
             "edge-container",
+            "edge-installer",
             "tar"
         ],
         "ppc64le": [