[BUG] Cross-Cluster Monitors do not allow wildcards in cluster names or index names

[bakert-96]

What is the bug?
During monitor creation, the user is not able to specify a wildcard for remote clusters or remote indices.

How can one reproduce the bug?
Steps to reproduce the behavior:

1. Set up two 2.12 clusters with Dashboards UI and test data that allow cross-cluster search (following the CCS documentation here and updating docker-compose to include Dashboards UI service).

2. Set the cluster setting plugins.alerting.remote_monitoring_enabled on the coordinating cluster to true

3. Navigate to the Create Monitor screen on the coordinating cluster (leave the default Per query monitor type and visual editor defining method) and click on the drop-down to select clusters. It correctly lists the local and remote clusters configured.
   

4. After typing in a cluster prefix with the wildcard *, no options are found.
   

5. After selecting the remote cluster from the cluster drop-down, the user is able to click on the indexes drop-down to select remote indices. It correctly lists the remote indices before and while typing an index name.
   

6. After typing in a remote index prefix with the wildcard *, no options are found.
   

The mappings are also not found after hitting enter and the user is not able to select a Time Field or do anything else that requires mappings.

What is the expected behavior?
We expected to be able to use a wildcard to specify clusters for the monitor. We also expected to be able to use a wildcard to specify remote indices after specifying the clusters.

Do you have any additional context?
We had some discussions with the OpenSearch team about this recently as we opened a PR to allow users to use wildcards when specifying remote clusters/indices. However, the OpenSearch team had created a feature for cross-cluster monitors with some additional requirements so they opted to make the changes on their end. In the discussions, we had asked if wildcards would be allowed when specifying remote cluster/index names and the OpenSearch team said it would be supported in their version. Are there plans to add this in the future?

If any additional info is needed, please let me know!