[Logs UI] Using cross cluster index not showing log data

[pnowak85]

Kibana version: 7.8.0

Elasticsearch version: 7.8.0

Browser version: Chrome 83.0

Browser OS version: Windows 10

Original install method (e.g. download page, yum, from source, etc.): official docker image

Describe the bug:
Logs UI does not show data from a cross cluster index, instead it shows: Looks like you don't have any logging indices. Let's add some!
Logs are definitely available, as Discover shows them.

Steps to reproduce:

1. Store logs via logstash (7.8.0 - new index) in a remote cluster (remote cluster still version 7.7.1)
2. Configure the remote cluster access in kibana (name e.g. metrics)
3. Check Discover for log entries from the remote cluster
4. Update Logs UI settings to access the remote cluster index e.g.: metrics:logstash-*
5. Open Logs UI - see Looks like you don't have any logging indices. Let's add some!

Expected behavior:
Show log data from the cross cluster index

Additional info
Did work in Kibana 7.7.1 / ES 7.7.1

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)

[weltenwort]

I have located the change that has probably introduced this in 7.8 and will create a fix shortly.