When the list of clusters is empty because none is configured, then the
UI was showing an endless spinner and a message saying it was waiting
for clusters.

This patch fixes that by initializing the clusters list as null and only
showing the "waiting" state until we get a clusters list result from the
server. If the list is empty, then an error message is shown.

We now have two ways in which one can login into a cluster either via
OIDC (if its configured for cluster) and via token.

Thus this patch creates a new component authbuttons whose job is to show
both buttons sign in and use token based on auth type received from
backend. We also make /login route to render the auth buttons instead of
token inputer.

Now we support client certificates, which means that the user may not
have to set up a token to authenticate against a cluster. In order to
understand whether the user needs a token, this patch does a quick
auth test in the login dialog, and if it fails then a token will be
required, otherwise the user is redirected to correct view.

This will make it easier to fetch a cluster's info by name which will
be needed when we make the auth token dependent on whether the cluster
needs it or not.

On authenticating input card we don't want to refresh the page instead
we would like to redirect the index route. This refreshing of page was
breaking the desktop app as well.

If there is only one single cluster configured, then we shouldn't show
its name in the authentication dialog (as it's used to distinguish
between cluster and that's not a problem when there's only one).

We will soon drop the "api" module, so for functions that have only one
caller, we're doing the request directly from the caller.

We want to reduce the redundancy in where to find the different cluster
related modules, so we're moving the useClusterConf hook to the
mentioned module.

We should make the mentioned text more clear and use the name of the
cluster that the user is authenticating against.

Now that we have an easy way to use a "cluster/root" style dialog, this
patch uses this new component (ClusterDialog) for the authentication.
This way the authentication dialog feels like a continuation of the
cluster chooser dialog.

We will soon have classes that represent K8s objects/resources, and
thus we move the api, apiProxy, and cluster modules into a new k8s
directoy (updating all the references to it), so things a bit better
structured.

Since now we support multiple clusters, we need to set up an
authentication token per cluster. So this patch changes how the
tokens are managed in order to address that.

Many places were not using strict equality, and thus it resulted in
lint warnings.