- correct source0/1 urls

- fix import path to the new upstream git repo
- Update to 5.16. Full upstream changelogs are at
https://discourse.ubuntu.com/t/lxd-5-16-has-been-released/37150
Highlights:
+ ISO volumes
+ IPAM information
+ selection of cluster groups when moving instances

- update keyring

- Update to 5.15. Full upstream changelogs are at
https://discuss.linuxcontainers.org/t/lxd-5-14-has-been-released/17259 and
https://discuss.linuxcontainers.org/t/lxd-5-15-has-been-released/17493
Highlights from 5.15:
+ Non-UEFI support in LXD VMs (CSM)
+ Instance rebuild
+ Container pinning based on NUMA nodes
+ User authentication information in API
Highlights from 5.14:
+ Cluster auto-healing
+ OIDC web authentication
+ lxc publish --reuse
+ Support for specifying the size of an LVM thinpool
+ Total disk and memory reporting