Upgraded openapi generator version to 5.1.0 for the support of nullable
values for optional fields; Added missing "Disabled" enum value to the
BootSourceOverrideEnabled model in the openapi schema.
Signed-off-by: James Gu <james.gu@att.com>
Change-Id: Ia3e0b018be13079d2085ef61ed2e797bcfd25fd7