Use meteortesting:mocha to allow headless client tests in CI

[jankapunkt]

Currently this template packages uses tinytest which is easy to use and straight forward. However, if we want to add CI we need to enable headless client tests, which tinytest does not support.

My proposed changes:

Use metertesting:mocha in combination with npm chai and puppeteer to run CI tests.
I would propose a PR, incuding the GitHub actions example.

[StorytellerCZ]

Looks like #11 is taking care of Tiny tests. But now that we have meteortesting under MCP we should take a look at it again. Though the question is if for packages having mocha isn't overkill (considering that most packages aren't big things).

[jankapunkt]

I think we can remain with tinytest, since zodern provided a package to easily spawn tinytest with puppeteer headless: https://github.com/zodern/mtest I will start to work on the CI

[jankapunkt]

Oh, I totally missed that the PR #11 already took this into account. This means we could easily setup these CI tests for other repos, too 🎉

[StorytellerCZ]

Hopefully. I will need to give this all update.

[StorytellerCZ]

Used the setup for Picker and it worked great.

[StorytellerCZ]

I'm wondering if we could somehow pair https://github.com/meteorengineer/setup-meteor and mtest @zodern