[ES UI Shared] Update isEsError function for new ES client

[yuliacech]

The helper function isEsError in es_ui_shared library needs to be updated as we move more plugins to the new ES js client. I think we would need to check for exception/error object to be intanceof ResponseError, which is returned by the client for 4xx and 5xx responses from ES (docs). We can then return a customError with message containing in e.body.error.reason. e.body is not yet typed, but should contain error object coming directly from the ES cluster:

{
    root_cause: string[];
    type: string;
    reason: string;
}

Migration docs link

[elasticmachine]

Pinging @elastic/es-ui (Team:Elasticsearch UI)