Add .dockerignore file to exclude build artifacts.

[nachomata]

This pull request adds a .dockerignore file to reduce the build context size and speed up the build process with Docker.

When building the Corteca CLI using Docker, it may take some extra time transferring the build context to the Docker daemon - especially due to the size of the dist directory with the build artifacts.

Performance comparison (personal scenario):

OS	Before	After
Windows	~30s to load build context (158.8 MB) + ~6s for COPY . .	~0.4s to load build context (14 KB) + ~0.6s for COPY . .
Linux (WSL)	~9s to load build context (166.51 MB) + ~12s for COPY . .	~0.5s to load build context (9.85 KB) + ~0.2s for COPY . .

I realize there may be additional files or directories that could also be added to the .dockerignore list. But to keep it simple and easy to review I only added the entries from the .gitignore, with primary focus on excluding the dist folder, as it is the largest contributor to the build context size.

Feedback is welcome!

[tsopokis]

LGTM