Unnecessary package dependencies

[TaoChenOSU]

This project takes hard dependencies on the following packages:

• Langchain: https://github.com/microsoft/opentelemetry-distro-python/blob/main/pyproject.toml#L30
• microsoft-agents-activity: https://github.com/microsoft/opentelemetry-distro-python/blob/main/pyproject.toml#L33
• microsoft-agents-hosting-core: https://github.com/microsoft/opentelemetry-distro-python/blob/main/pyproject.toml#L34

These packages are unnecessary will pollute the uses' environments.

[hectorhdzg]

@TaoChenOSU langchain is an optional dependency now (#80)
We will follow up with other two after stable release