Follow up from https://jira.magnolia-cms.com/browse/MAGNOLIA-7358

Problem: 

Issue was discovered when investigating rendering performance issue in instance with node_modules directory in light module (brought in by use of webpack) and it containing additional 30K files (facepalm). This fact, together with multiple calls to resfn in single template lead to performance issue (traversing of 40K files while searching for resources took approx 2 seconds).

Improvement suggestion:

• reference to comment link: this is a different issue. However, it is also an understandable one and can be possibly addressed by altering the property magnolia.resources.filesystem.observation.excludedDirectories, which should contain comma-separated list of directories to be not included into FS resource origin (I am not sure if that property supports *-templates tho, if not - we should add such support).
• https://git.magnolia-cms.com/projects/PLATFORM/repos/main/pull-requests/1376/overview?commentId=122700 : From a more general point of view, while this approach works, I'm not sure how useful it is to a developer of a light module. Such a developer cannot easily change these properties. I think we need another approach in addition to the changes in this PR that allow a developer of a light module to configure exclusions from the light module itself. Let's create a separate ticket for this as needed.