Added a Dockerfile to starting a REPL for testing purposes

[mridang]

Which Problems Are Solved

• Manual REPL Setup: Developers previously had to manually configure and launch a REPL environment with the Zitadel library preinstalled.
• Inconsistent Development Environments: Without a standardized environment, differing local setups led to configuration issues and increased onboarding time.
• Slower Iteration Cycles: The lack of an automated, preconfigured REPL slowed down testing and experimentation with library changes.

How the Problems Are Solved

• Docker Integration: Dockerfiles have been added for various languages (Java, PHP, Python, Ruby), enabling developers to quickly spin up a container with a fully built and preloaded Zitadel library.
• Preconfigured REPLs: Each Dockerfile launches a language-specific REPL (e.g., JShell for Java, PsySH for PHP, IPython for Python, IRB for Ruby) with the library already installed. This removes the need for manual setup.
• Standardized Environment: Using Docker ensures that every developer uses the same development environment, reducing "works on my machine" issues and speeding up the development cycle.

Additional Changes

• Updated documentation to include build and run instructions for the new Docker containers.
• Added example commands to the README to help new contributors quickly start a REPL with the Zitadel library.
• Made minor build process adjustments to ensure seamless Docker integration.

Additional Context

None