With more than 3 arches applications pip install -e ... is not supported

[jacobtylerwalls]

After #11016, when projects became arches applications also (i.e. "Arches Application" = "anything built with arches"), @chiatt found an issue with these four applications installed, most of them with pip install -e in editable mode:

• Disco
• Arches for Science
• Arches Templating
• Dashboard (https://github.com/chiatt/dashboard)

Currently we only support up to three arches applications for editable installs; any application after the fourth is assumed to exist only in site-packages, the regular pip install location.

The reason for this is that load-component-dependencies.js has two dynamic components: the component name (e.g. report.js) and the arches application name. Webpack supports at most one dynamic component. In other words, it needs to be told where to look, and editable project locations could be anywhere on your filesystem. (You don't want Webpack to crawl your whole system anyway.)

We could explore trying to expose a setting like EDITABLE_PROJECTS_FOLDER and tell webpack to look there, but the quick fix is to just increase the limit from 3 to somewhere around 8 or 9.