[ML] Add remote cluster license check to Validate Job

[LucaWintergerst]

When creating an ML job, the Validate function allows to run a set of pre-flight checks to ensure that a job will work as expected.
However, this check does not verify that a remote cluster has a sufficient License

The ML team thinks that some additional work on the ES side will be required to expose this to kibana. See elastic/elasticsearch#37858

Steps to reproduce:

launch 1 node, cluster_a with platinum/trial license
launch 1 node, cluster_b with a basic license
add CCS settings to cluster_a
add ccs index pattern to cluster_a
create advanced job using ccs pattern, click on validate -> all green
attempt to start the job -> it won't run

[elasticmachine]

Pinging @elastic/ml-ui

[davidkyle]

A good first step that wouldn’t require lots of additional work would be to warn and document the licence requirements if CCS is used. At least then user won’t be so surprise when the job fails.