Refactor to use config, fix pipeline example

Changes to simplify gemini-agents-toolkit dev set up:

created a config for setting up values from envs and constants, refactored code to use the config
added a new os envs GOOGLE_PROJECT and GOOGLE_REGION
fixed a bug in EagerPipeline example
added a missed lib to requirements
updated version to 2.3.0 (partially compatible, os environment expects a new env GOOGLE_PROJECT with gcp project name)

GeminiAgentsToolkit / gemini-agents-toolkit