feat(instrumentation): Updated Langchain instrumentation to use Langchain Callbacks

[midhun1998]

This is a draft PR to record my progress and collaborate with the team to get suggestions.

Supposed to fix #541

I will check the below checkbox when they are ready:

• [ ] I have added tests that cover my changes.
• [ ] If adding a new instrumentation or changing an existing one, I've added screenshots from some observability platform showing the change.
• [x] PR name follows conventional commits format: feat(instrumentation): ... or fix(instrumentation): ....
• [ ] (If applicable) I have updated the documentation accordingly.

[CLAassistant]

All committers have signed the CLA.

[midhun1998]

Note:

• I know some changes should not go into the final PR. Please bear with me.
• I will be squashing all the commits as well

I will clean it up before marking this as ready.

Thanks! 😇