Acceptance tests using pre-installed apps_paths

[phil-davis]

PR #30889 issue #29839 introduced apps-external as a second apps path on a default installation.

• review existing appmanagement.feature scenarios to see if they are still "a good thing"
• add scenarios to confirm the new default path works
• whatever else might be useful related to this for testing ;)

[ownclouders]

GitMate.io thinks possibly related issues are #22485 (test), #31579 (test), #22492 (test), #33690 (cleanup acceptance tests WebDav trait), and #31516 (Acceptance test coding standard changes).

[mmattel]

References #34898 (Add the apps-external directory during setup only)

[skshetry]

@phil-davis, I added a few tests, but as the issue is more towards testing installation folder and check where the apps is written to, we need some better way to simulate an actual app install. We might need to use core api's and simulate/emulate installs through use of our custom api's in testing app.

Needs more research.