exclude metadata.json file

[AnnMarieW]

Based on this discussion at Plotly, it's OK to exclude the metadata.json file which will reduce the package size significantly.

We started be minifying the metadata.json file in #347 which reduced the file size from 5MB to 3MB. This PR excludes the file.

Also included some new files that were added when setting up testing and the PyCafe hosting in MANIFEST.in. This ensures the tar.gz file can be installed without errors.

I tested this by running:

• npm run build
• npm run dist

installed the tarball in a new venv
ran a sample app - everything worked fine :tada

[alexcjohnson]

This works, but it's a little funny to include *.json above and then exclude this one. The result of those two together is just to include dash_mantine_components/package-info.json so it would be cleaner to just include that file by itself.

While we're at it, it's also redundant (but common across most dash component suites) that we include both package.json and dash_mantine_components/package-info.json since these are identical (package.json is copied to dash_mantine_components/package-info.json during build). The former is referenced in setup.py to pull information into the pypi record, the latter in dash_mantine_components/__init__.py to get the package name and version, and I believe that's it. This file isn't very big, but we should be able to remove package.json entirely if we point setup.py to the other one.

[alexcjohnson]

💃 LGTM - one nonblocking comment.