Add support of tpu-client-next to validator

[KirillLykov]

Problem

Current quic client implementation ConnectionCache has some disadvantages:

• traffic fragmentation
• complex implementation using locks

Validator uses quic client for two components:

1. Forwarder
2. SendTransactionService

This issue to is track the work on adding support of new network crate tpu-client-next to the these components.
When finished, it should be possible to choose between two client codes.

Proposed Solution

• Extract network-related code from SendTransactionService into a separate structure Extract client code in send_transaction_service into a new structure #3423
• Add a new client support to SendTransactionService, instrument all the related tests with new client as well use tpu-client-next in send_transaction_service #3515
• Verify that backport PRs merged: v2.1: Extract client code in send_transaction_service into a new structure (backport of #3423) #3480 and (after) v2.1: use tpu-client-next in send_transaction_service (backport of #3515) #3884
• Add a new client to validator Use tpu client next in validator with receiver #3893
• Add tpu-client-next to ForwardingStage (new implementation of forwarding by Andrew), poc is poc for use tpu client next forwarding #3286
• Probably add some implementation of the same to the Forwarder since it is unclear when ForwardingStage will be released
• Add multi node fan out parameter to the tpu-client-next add fanout to tpu-client-next #3478
• Add equivalent of ConnectionCache warm-up service to the tpu-client-next add fanout to tpu-client-next #3478
• Add tests for set_identity Add set_identity tests #3794,
• Modify this test to work with flag use_tpu_client_next.

[KirillLykov]

Address #3515 (comment)

[KirillLykov]

Address #3515 (comment) (outside of backporting)

[KirillLykov]

Backport to 2.1

For the sake of backporting to 2.1, do the following:

• Revert PR_3: Revert "send-transactions: optimize retry pool" #4250 . The original PR: send-transactions: optimize retry pool #31
• Revert PR_2: Revert "use tpu-client-next in send_transaction_service (#3515)" #4252 . The original PR: use tpu-client-next in send_transaction_service #3515
• Revert PR_1: Revert "Extract client code in send_transaction_service into a new structure" #4254 . The original PR: Extract client code in send_transaction_service into a new structure #3423
• Add back PR_1: Reapply changes from reverted PR 3423 #4257 with changes minimizing API changes, see aed704e
• Add backport for PR_1
• Add back PR_2: Reapply changes from reverted PR 3515 #4261 with minimizing API changes (use new/new_with_client)
• Add backport for PR_2
• Add backport for PR_3 (not sure if needed, but there is PR_4 on top, so to avoid possible conflicts better to add. Or add it later on top of PR_4).