Discuss using the root dir as Docker's build context

[sodic]

Version: 0.16.4

When users build the server with docker build, we expect them to use the .wasp/build directory as Docker's build context. This is probably unexpected for many users. They'd expect to run docker build from the root directory (thanks for reporting @fbozic).

Issue #2837 covers documenting this behavior.
This issue is about investigating the issue further and possibly moving the build to the project's root.

There are some constraints making this more difficult. The details are decribed here: #1769 (comment)