task index: fix return schema annotations

task index: fix return schema annotations

both task sources use PVE::Tools::upid_decode, which ensures all of the
':' delimited fields are set.

this only leaves 'status' and 'endtime' as optional, which are not set
for currently running tasks.

reorder them in the code for easier matching with their on-disk format.

Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
Acked-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Reviewed-by: Thomas Lamprecht <t.lamprecht@proxmox.com>