default bases don't include jammy

[Jordan Barrett]

We are noticing in Juju 3.0 that when deploying certain charms, they default to focal instead of jammy. This is strange because deployed machines default to jammy on Juju 3.0.

We've looked into it and think there's a bug in the Charmhub API. We're making a request to the API with
```
"base":{"architecture":"amd64","name":"NA","channel":"NA"}
```
to try and get the supported bases for the charm. For some reason, it's not returning jammy in the list of default bases, even though the charm supports jammy (and Charmhub info API says that it supports jammy too).
```
"default-bases":[{"architecture":"amd64","channel":"18.04","name":"ubuntu"},{"architecture":"amd64","channel":"20.04","name":"ubuntu"}]
```
We've noticed this with both the `juju-dashboard` charm and the `tiny-bash` charm. The logs below should give some more context with our request and the response from Charmhub.
```
machine-0: 16:12:30 TRACE juju.apiserver.charms.charmhubrepo.client charmhub POST request POST /v2/charms/refresh HTTP/1.1
Host: api.charmhub.io
Accept: application/json
Content-Type: application/json
User-Agent: Juju/3.0.1

{"context":[],"actions":[{"action":"install","instance-key":"10bba603-4da0-4fb6-80c1-c2f1388ef79f","name":"tiny-bash","channel":"stable","base":{"architecture":"amd64","name":"NA","channel":"NA"}}],"fields":["bases","config-yaml","download","id","license","metadata-yaml","name","publisher","resources","revision","summary","type","version"]}

machine-0: 16:12:30 TRACE juju.apiserver.charms.charmhubrepo.client charmhub POST response HTTP/1.1 200 OK
Content-Length: 531
Content-Type: application/json
Date: Tue, 01 Nov 2022 15:12:30 GMT
Server: gunicorn/20.0.4
Snap-Store-Version: 50
X-Request-Id: 3EA8230BD3E40A83255C01BB6361375E49A5CB45
X-Vcs-Revision: 9a1852f6
X-View-Name: snapdevicegw.webapi_refresh_charm.charm_refresh

{"error-list":[],"results":[{"charm":null,"error":{"code":"invalid-charm-base","extra":{"default-bases":[{"architecture":"amd64","channel":"18.04","name":"ubuntu"},{"architecture":"amd64","channel":"20.04","name":"ubuntu"}]},"message":"Instance key '10bba603-4da0-4fb6-80c1-c2f1388ef79f' invalid 'base' in 'install' for charm_id=URvt1LraV3i6PhhfLNsFF3GDHzzPPuaq name=tiny-bash"},"id":"URvt1LraV3i6PhhfLNsFF3GDHzzPPuaq","instance-key":"10bba603-4da0-4fb6-80c1-c2f1388ef79f","name":"tiny-bash","released-at":null,"result":"error"}]}
```

[Daniel Manrique (roadmr)]

I’m fairly sure it’s going to be the hardcoded list of LTSes in (devicegw? snaprevs?) which considers Focal the most recent LTS we give out. We need to clear the decision with the Juju team but the fix is likely going to be adding Jammy to that list and making Jammy the preferred/default Ubuntu release / base.

[Jonathan Hartley (tartley)]

Agreed with Daniel's assessment.

[Jordan Barrett (barrettj12)]

That sounds like the right fix. I think we still want to default to focal on 2.9, but we can do that on the Juju end.

[Guillermo Gonzalez (verterok)]

Hi Jordan,

do we need to wait for a 2.9.x release before doing our side of the changes?

Thanks

[John A Meinel (jameinel)]

My position is that a Juju *controller* should default to Focal for 2.9, but as 2.9 does support Jammy as a target, it is fine for a charm that says it wants to be deployed on Jammy to do so, even with 2.9.

[Heather Lanigan (hmlanigan)]

I don't believe that juju should rely on the order of bases in the manifest. Either juju chooses based on criteria defined, (there is a juju bug I need to file) or the charm author can define a preferred base. However it should be explicit, not based on a order than most authors never really knew about.