chore: declare 26.04 support

[wallyworld]

Add 26.04 support in charmcraft.yaml

Includes adding the model config for agent-stream=proposed on k8s for the pre-merge smoke tests because we are installing juju from the candidate channel, and if we do that and there is a candidate release there, we need to ensure k8s is able to get the candidate oci image as well.

We also need to use charmcraft 4.1 from edge to get the 26.04 support. This can be changed when charmcraft 4.1 is fully released.

juju bootstrap lxd --config image-stream=daily --bootstrap-base ubuntu@26.04 --controller-charm-channel=latest/edge/racoon-support-dde783b2b3b3148f835d6c4afa1ba26f756b2a65 --force

Model       Controller           Cloud/Region         Version  Timestamp
controller  localhost-localhost  localhost/localhost  3.6.14   10:19:14+10:00

App         Version  Status  Scale  Charm            Channel                                                              Rev  Exposed  Message
controller           active      1  juju-controller  latest/edge/racoon-support-dde783b2b3b3148f835d6c4afa1ba26f756b2a65  183  yes      

Unit           Workload  Agent  Machine  Public address  Ports      Message
controller/0*  active    idle   0        10.68.47.74     17022/tcp  

Machine  State    Address      Inst id        Base          AZ          Message
0        started  10.68.47.74  juju-38d4e0-0  ubuntu@26.04  wallyworld  Running

juju bootstrap microk8s --config agent-stream=proposed --controller-charm-channel=latest/edge/racoon-support-dde783b2b3b3148f835d6c4afa1ba26f756b2a65
Creating Juju controller "microk8s-localhost" on microk8s/localhost
Bootstrap to Kubernetes cluster identified as microk8s/localhost
Creating k8s resources for controller "controller-microk8s-localhost"
Starting controller pod
Bootstrap agent now started
Contacting Juju controller at 10.152.183.121 to verify accessibility...

Bootstrap complete, controller "microk8s-localhost" is now available in namespace "controller-microk8s-localhost"

Now you can run
        juju add-model <model-name>
to create a new model to deploy k8s workloads.

Model       Controller          Cloud/Region        Version  SLA          Timestamp
controller  microk8s-localhost  microk8s/localhost  3.6.15   unsupported  11:13:44+10:00

App         Version  Status  Scale  Charm            Channel                                                              Rev  Address  Exposed  Message
controller           active      1  juju-controller  latest/edge/racoon-support-dde783b2b3b3148f835d6c4afa1ba26f756b2a65  182           yes      

Unit           Workload  Agent  Address     Ports      Message
controller/0*  active    idle   10.1.78.89  37017/TCP