Add Java and C++ TCP server concept slugs

[andy1li]

And add concept_slugs to stage #ih0 (Extract URL path):

Note

Adds java-tcp-server and cpp-tcp-server concept slugs to several stages and introduces a concept_slugs block for ih0.

• Course definition (course-definition.yml):
  • Add java-tcp-server and cpp-tcp-server to concept_slugs for stages: at4, ia4, ej5.
  • Add concept_slugs to stage ih0, including java-tcp-server and cpp-tcp-server (along with existing TCP server concepts).

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