simplified-installer: do not mandate FDO section in simplified provisioning

- build simplified installer iso without mentioning FDO section.
  - change done for rhel8 and rhel9
  - add test case for this use case in test/case/ostree-simplified-installer.shovisioning
  - fixed review comments

Signed-off-by: Sarita Mahajan <sarmahaj@redhat.com>

internal/blueprint/customizations.go

@@ -380,3 +380,7 @@ func (c *Customizations) GetOpenSCAP() *OpenSCAPCustomization {
 	}
 	return c.OpenSCAP
 }
+
+func (f *FDOCustomization) HasFDO() bool {
+	return f != nil
+}