Unbreak devcontainer

[finnless]

Codespaces and devcontainer was broken by the repo restructure.

• Description: Add libs/langchain to container so it can be built without error.
• Issue: -
• Dependencies: -
• Tag maintainer: @hwchase17 @baskaryan
• Twitter handle: @finnless

The failed build log says:

#10 [langchain-dev-dependencies 2/2] RUN poetry install --no-interaction --no-ansi --with dev,test,docs
#10 sha256:e850ee99fc966158bfd2d85e82b7c57244f47ecbb1462e75bd83b981a56a1929
2023-07-23 23:30:33.692Z: #10 0.827 
#10 0.827 Directory libs/langchain does not exist
2023-07-23 23:30:33.738Z: #10 ERROR: executor failed running [/bin/sh -c poetry install --no-interaction --no-ansi --with dev,test,docs]: exit code: 1

The new pyproject.toml imports from libs/langchain:

langchain/pyproject.toml

Lines 14 to 16 in 77bf75c

	[tool.poetry.group.docs.dependencies]
	langchain = { path = "libs/langchain/", develop = true }
	autodoc_pydantic = "^1.8.0"

But libs/langchain is never added to the dev.Dockerfile:

langchain/libs/langchain/dev.Dockerfile

Lines 37 to 39 in 77bf75c

	# Copy only the dependency files for installation
	COPY pyproject.toml poetry.toml ./

[baskaryan]

thanks @finnless!