Improve "Kibana server not ready yet" message

[ppf2]

Kibana version: 6.5.0

When migrating Kibana objects (regardless of whether it ended up being successful, or failed requiring manual intervention to clean up incremental .kibana-N index), we simply specify a "Kibana server not ready yet" error on the UI.

Ideally, it will be great for the UI to stream the Kibana log to the UI to provide more details to the end user on what is happening. If there is no such facility today for Kibana to display its own server log, it will at least be helpful to have a better message instructing the end users to review/tail the Kibana server log for more information :)

Solution:
#26039 (comment)

[elasticmachine]

Pinging @elastic/kibana-operations

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)

[rudolf]

Before we can expose server logs to a user, we need authenticate/authorize the user, but when the Kibana server isn't ready, security also isn't ready. However, we can provide a bit more detailed status by exposing Core services' status from the WIP status service #41983

This would allow us to show that the savedobjects-service is unavailable with some more detail like that we're waiting for migrations to complete or even current migration progress.

[rudolf]

Related to #52202

[pgayvallet]

reassigning to @elastic/appex-sharedux

FWIW this is still what we have today when trying to access Kibana while it cannot connect to ES:

[petrklapka]

Assigned to Kate and Kevin to take a peek if this is feasible, or desired. It's an old issue that never got traction, and there may be a lot of complexity for little return. Don't be afraid to determine as a "will not do".

[kevinsweet]

How about a simple text change @ek-so @petrklapka?
Kibana server not available, an update may be in progress. Check Kibana server logs for more details.

I'm thinking it's a bit more context, and in some cases more accurate (the "yet" implies non failure, which we don't know).

@petrklapka I assume any additional UI treatment even if very basic would be difficult considering we can't render Kibana?

Even if we could, I don't think we should stream logs as part of a loading message, we should direct them to the proper place.

[ek-so]

Also for the context — we had somewhat similar issue recently:
https://github.com/elastic/kibana-team/issues/948#event-13364920197
There was also no option to add illustrations or more complex css, but it would be nice if we can reuse that simple UI here as well.

As for the text I like it. A question though: are we able to split those reasons for the server to be not ready:

When migrating Kibana objects (regardless of whether it ended up being successful, or failed requiring manual intervention to clean up incremental .kibana-N index), we simply specify a "Kibana server not ready yet" error on the UI.

If yes, it might be different text for those two cases.
And also, I assume "Reload" button doesn't help here in any case, so we can remove it (or it may help?)

[petrklapka]

I think Kevin's copy and the same design Kate linked should be enough of an improvement here.
I would recommend keeping the reload button. After all, that is what the user needs to do... reload the page. Making it easier for them with a big friendly blue button will make it more convenient. Let's queue this up!