[Guided onboarding] Handle missing permissions

[yuliacech]

If the user doesn't have permission to create or change saved objects that hold the state for guided onboarding, some API requests will fail and the UI will display an error. We should check for the needed permissions when handling the API requests and correctly display a message about missing permissions in the UI.

How to reproduce

1. Create a role with Kibana access and give it a permission to only access for example Dev Tools in Kibana.
2. Create a user and add the role, then log in with the user.
3. Click the button "Setup guide" that will display the dropdown panel with an error (see screenshot below).

[elasticmachine]

Pinging @elastic/platform-onboarding (Team:Journey/Onboarding)

[lukeelmers]

How visible do we want to make this failure -- are we certain we need to surface this error to users at all? I'm wondering if it wouldn't be better to hide the guided onboarding entirely if a user doesn't have the right permissions, or perhaps store a user's progress in local storage as a fallback for when they don't have the right permissions.

We should check for the needed permissions when handling the API requests and correctly display a message about missing permissions in the UI.

Since this scenario is an expected state for many users, I would consider either doing this check entirely on the server (& returning a 200 to the client with instructions on what to render in that case), or exposing a separate route to perform the authz check and then returning 403 from the existing route in case you forget to do the check. That way the Kibana APIs aren't constantly filling the logs with errors.