build: Add .dockerignore to optimize Docker build context

[Prasanjeet-Microsoft]

Purpose

• This PR adds a ".dockerignore" file to prevent unnecessary files and directories (such as virtual environments, build artifacts, logs, node_modules, and IDE configs) from being sent to the Docker daemon during image builds.

• Optimizing the build context improves performance and reduces image size and build time.

Does this introduce a breaking change?

• Yes
• No

How to Test

• Get the code

git clone [repo-address]
cd [repo-name]
git checkout [branch-name]
npm install

• Test the code

What to Check

Verify that the following are valid:

• Confirm .dockerignore is present at root directory.
• Ensure expected files (e.g. .git, node_modules, __pycache__, etc.) are excluded from build context.
• Run a Docker build and verify only necessary files are included.
• Confirm no unintended exclusions (like source code or Dockerfile used for build)