Add trailing / to ubuntu: and ubuntu-daily: remotes to avoid redirects

[simondeziel]

Of the 4 builtin remotes, 2 don't have a trailing /:

$ lxc remote list -f csv | awk -F, '/^ubuntu/ {print $2}' | grep -v /$
https://cloud-images.ubuntu.com/releases
https://cloud-images.ubuntu.com/daily

They should probably have one to avoid a permanent redirection (301):

$ wget -qSO /dev/null https://cloud-images.ubuntu.com/releases 2>&1 | grep -E 'HTTP/|Location'
  HTTP/1.1 301 Moved Permanently
  Location: https://cloud-images.ubuntu.com/releases/
  HTTP/1.1 200 OK

$ wget -qSO /dev/null https://cloud-images.ubuntu.com/daily 2>&1 | grep -E 'HTTP/|Location'
  HTTP/1.1 301 Moved Permanently
  Location: https://cloud-images.ubuntu.com/daily/
  HTTP/1.1 200 OK

[github-actions]

Heads up @mionaalex - the "Documentation" label was applied to this issue.