Add .npmignore to reduce package size

[forest1102]

Is your feature request related to a problem? Please describe.
I'm always frustrated when the npm package size is larger than necessary due to included files that aren't required for production.

Describe the solution you'd like
Adding a .npmignore files in each packages to exclude unnecessary files (e.g., image_snapshots, docs, configs) from the npm package to reduce its size. Especially, image files in __image_snapshots__ has unnecessarily big file size and long filename which can cause too long filename error when copying.

Describe alternatives you've considered
An alternative would be to manually specify files to include in the package.json, but using .npmignore is more flexible and easier to maintain.

Additional context
Reducing the package size will improve installation speed and reduce bandwidth usage for users.