[BUG] Removing String format in RemoteStoreMigrationAllocationDecider

[RS146BIJAY]

Describe the bug

Description

String.format is a relatively expensive operation for concatenating strings. Inside RemoteStoreMigrationAllocationDecider, the function calls to String.format stands out as the most resource-intensive operation in terms of latency.

Related component

Indexing:Replication

To Reproduce

Create 500k shards on a setup with 1000 data nodes and 3 master nodes.

Expected behavior

Improves the latency of RemoteStoreMigrationAllocationDecider by replacing calls to String.format with more efficient StringBuilder for string concatenation

Additional Details

Plugins
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Host/Environment (please complete the following information):

• OS: [e.g. iOS]
• Version [e.g. 22]

Additional context
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