feat: add sa token component to kfp-persistence

[DnPlas]

The kfp-persistence charms needs a ServiceAccount token to be inside the workload container to be able to start the service. The sa token component will generate the required token and save it in a file where it can be accessed to later be pushed from the charm to the workload container.

Testing

1. Build and deploy the charm in this PR
2. Using kubectl exec check the files inside the workload container. Make sure you check the persistenceagent container and not the charm.
3. There must be a non empty token file in /var/run/secrets/kubeflow/tokens/<token name>

Fixes #343

[orfeas-k]

So left one more comment which is more of base charm question as to if this should be the way to implement the component. The logic in the rest of the code looks good.

I will go ahead and deploy charms from the PR in order to verify the functionality. My understanding is that I should:

• look for the file that the component is expected to create
• check if kfp-persistence service has started successfully

Is there something else I should look into?

[DnPlas]

So left one more comment which is more of base charm question as to if this should be the way to implement the component. The logic in the rest of the code looks good.

I will go ahead and deploy charms from the PR in order to verify the functionality. My understanding is that I should:

* look for the file that the component is expected to create

* check if kfp-persistence service has started successfully

Is there something else I should look into?

Hey @orfeas-k, I added a "testing" section in the description of the PR. Regarding checking that the service starts, in this case, we'll see the service starting just fine because in pipelines 2.0.0-alpha.7 it does not need this file. We will observe this dependency when we finalise the work in #331. For now just ensuring the file is there is enough.

[orfeas-k]

Great work and collaboration @DnPlas, approving!