Baler directory check strictness

[wigman]

Request to loosen up findMagentoRoot check requirements.

Currently Baler checks for these required directories:

• app/
• pub/
• lib/
• index.php

However, index.php is not necessary, while vendor probably is necessary (for the graph building later on).

The baler build should preferably only check for pub/static/frontend because that's the only place it needs to get data from, and it's enough to determine you are in the right directory.

For the baler graph method (when released) you could do a wider check, including the other directories.

1 - The error message could be more descriptive (currently says Could not find Magento store root from [X].
2 - The requirements could be reduced

Why is this important?

A lot of us devs out there use docker and run npm commands locally, not in the containers. So we usually don't have all these directories locally mounted/synced to the containers.
Especially lib/ and index.php are very rare to have synced.