[UI] Select regions for federated search

[hengfeiyang]

Which OpenObserve functionalities are relevant/related to the feature request?

log search

Description

We need add region filter on the logs page with super cluster.

i already added the API for list regions:

GET /api/clusters

{
	"us-east-1": [
		"dev3"
	],
	"us-west-2": [
		"dev4"
	]
}

The key is region name, the value is the clusters in the region.

Proposed solution

Alternatives considered