Test production build on CI

[cprecioso]

Right now we only test wasp build manually on the template-test directory.
We should add build tests to our CI so that we don't need to do it manually.

[wang2-lat]

We should add a CI job that runs wasp build on template-test (and maybe a few other test projects) to catch build regressions automatically—could use GitHub Actions with a matrix strategy to test multiple templates in parallel.