feat(interactive): Implement service register and primary election

[zhanglei1949]

• Introduce etcd-cpp-api-v3 and cpprestsdk as submodule dependencies.
• Implement ServiceRegister which registers the server itself to the etcd-based service registry.
• Implement the primary election by using etcd as a distributed lock: whoever first puts the primary key-value pair, is the master.
• In the later PR, we should implement the promote() function, which should be called after adding the primary key-value pair succeeds.

[github-actions]

Please check the preview of the documentation changes at
https://e9ab5ffc.graphscope-docs-preview.pages.dev

[Copilot]

Pull Request Overview

This PR introduces a new integration test for the service registry and primary election features by adding a dedicated CI job in the GitHub Actions workflow.

• Adds a new "test-service-registry" job to validate the etcd-based service registry and primary election via a series of scripted steps.
• Configures the environment, downloads and launches etcd, executes the interactive_server, and validates key outputs.

Files not reviewed (15)

• .gitmodules: Language not supported
• flex/CMakeLists.txt: Language not supported
• flex/cmake/BuildEtcdCpp.cmake: Language not supported
• flex/engines/http_server/CMakeLists.txt: Language not supported
• flex/engines/http_server/actor/admin_actor.act.cc: Language not supported
• flex/engines/http_server/graph_db_service.cc: Language not supported
• flex/engines/http_server/graph_db_service.h: Language not supported
• flex/engines/http_server/service_register.cc: Language not supported
• flex/engines/http_server/service_register.h: Language not supported
• flex/storages/rt_mutable_graph/schema.cc: Language not supported
• flex/storages/rt_mutable_graph/schema.h: Language not supported
• flex/third_party/cpprestsdk: Language not supported
• flex/third_party/etcd-cpp-apiv3: Language not supported
• flex/utils/service_utils.cc: Language not supported
• flex/utils/service_utils.h: Language not supported

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 44.76%. Comparing base (d39709a) to head (1d350b0).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4589   +/-   ##
=======================================
  Coverage   44.76%   44.76%           
=======================================
  Files          12       12           
  Lines         592      592           
=======================================
  Hits          265      265           
  Misses        327      327           

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update d39709a...1d350b0. Read the comment docs.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[github-actions]

/cc @yecol @sighingnow, this issus/pr has had no activity for a long time, please help to review the status and assign people to work on it.