[server][controller][dvc][changelog] Avoid constructing D2Client for server, controller and clients.

[haoxu07]

Problem Statement

Previously, each component (server, controller, change_capture_client) constructed its own D2Client instance using D2Builder and passed in the necessary configurations. As the D2Client continues to evolve, it now requires additional configuration parameters, some of which are unnecessary or unavailable in test and open-source environments. To address this, we refactor the components to accept pre-constructed D2Client instances instead of constructing them internally.

This change allows the deployable layer to construct fully customized D2Clients suited to the environment and usage, improving flexibility and testability.

Affected Components:

• Server
• Controller
• DaVinci Client
• Change Capture Clients

Solution

Code changes

• Added new code behind a config. If so list the config names and their default values in the PR description.
• Introduced new log lines.
  • Confirmed if logs need to be rate limited to avoid excessive logging.

Concurrency-Specific Checks

Both reviewer and PR author to verify

• Code has no race conditions or thread safety issues.
• Proper synchronization mechanisms (e.g., synchronized, RWLock) are used where needed.
• No blocking calls inside critical sections that could lead to deadlocks or performance degradation.
• Verified thread-safe collections are used (e.g., ConcurrentHashMap, CopyOnWriteArrayList).
• Validated proper exception handling in multi-threaded code to avoid silent thread termination.

How was this PR tested?

• New unit tests added.
• New integration tests added.
• Modified or extended existing tests.
• Verified backward compatibility (if applicable).

Does this PR introduce any user-facing or breaking changes?

• No. You can skip the rest of this section.
• Yes. Clearly explain the behavior change and its impact.