openstack-origin=distro is set for focal-yoga

The charm from yoga track for focal should have cloud:focal-yoga instead of "distro". Otherwise, unexpected version of Octavia (Ussuri) is deployed for Yoga environment.

$ juju info --series focal --arch amd64 octavia | grep yoga
  yoga/stable: 3026201 2022-05-05 (71) 39MB
  yoga/candidate: ^
  yoga/beta: ^
  yoga/edge: ^

$ juju download --series focal --arch amd64 --channel yoga/stable octavia
Fetching charm "octavia" using "yoga/stable" channel and base "amd64/ubuntu/20.04"
Install the "octavia" charm with:
    juju deploy ./octavia_9f26dd0.charm

$ unzip -q -d octavia octavia_9f26dd0.charm

$ grep -A1 '"openstack-origin":' octavia/config.yaml
  "openstack-origin":
    "default": "distro"

^^^ "distro". this is expected to be "yoga".

Other charms for example, keystone has the expected value.

$ juju info --series focal --arch amd64 keystone | grep yoga
  yoga/stable: 572 2022-06-15 (572) 781kB
  yoga/candidate: ^
  yoga/beta: ^
  yoga/edge: ^

$ juju download --series focal --arch amd64 --channel yoga/stable keystone
Fetching charm "keystone" using "yoga/stable" channel and base "amd64/ubuntu/20.04"
Install the "keystone" charm with:
    juju deploy ./keystone_e0108fd.charm

$ unzip -q -d keystone keystone_e0108fd.charm

$ grep -A2 'openstack-origin:' keystone/config.yaml
  openstack-origin:
    type: string
    default: yoga

^^^ "yoga"