chapters/exploitation-techniques: Add Dockerfile for 08-challenge-shellcode-after

[gabrielmocanu]

Description:

Create a Dockerfile for 08-challenge-shellcode-after exercise.

Requirements:

1. Use a multi-stage Dockerfile:

• Build Stage:
  - Compile the provided C code into an executable.
• Runtime Stage:
  - Run the compiled executable and ensure it listens or operates on port 31346.

2. Verify the functionality of the solution to ensure that it works as expected after building and running the Dockerfile.

3. Ensure the Dockerfile is optimized and avoids unnecessary layers.

Expected Outcome:

A fully working Dockerfile that can be built and executed in two separate stages, satisfying the above requirements.