Commit Message:
OdCdsApi interface is introduced as an API used for the on-demand discovery. The implementation of it is provided using the CdsApiHelper class, so OdCdsApiImpl handles the discovered cluster in the same way as CdsApiImpl does. On the ClusterManagerImpl side, the discovery manager (ClusterDiscoveryManager) is added to help in deduplicating the requests for the same cluster from within the same worker thread. Further deduplication of the requests coming from different worker threads is done in ClusterManagerImpl in the main thread. Each unique request for a cluster also receives a timeout to catch a case when a discovery fails, thus allowing to let the worker threads to handle the failure.

Additional Description:
This is a continuation of #15857 - I could not reopen it, so I'm opening a new PR. I used the opportunity to rebase my changes on top of main.

Risk Level:
Low. A new feature not wired up anywhere yet.

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