Refactor: etcdserver-move rafthttp.Transport initialization to bootstrap

[carpewang]

Descriptions:

• This PR addresses the existing TODO comment in the NewServer function:// TODO: move transport initialization near the definition of remote.
• This PR refactors the server initialization process by decoupling the Raft consensus component from the initial bootstrap phase. Previously, Raft was initialized within the bootstrap function, which tightly coupled cluster setup with consensus mechanics.

Changes Include:

• Moved the initialization and startup of rafthttp.Transport into the bootstrap() function.

• The transport instance is now part of the returned bootstrappedServer struct.

• Refactored NewServer() to simply assign the bootstrapped transport and wire it up.

[k8s-ci-robot]

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This pull-request has been approved by: carpewang
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[k8s-ci-robot]

Hi @carpewang. Thanks for your PR.

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