Add FileObserver to detect local file change

Description

Add FileObserver on user's media directory.

Issue(s)

closes https://gitlab.e.foundation/e/os/backlog/-/issues/2

Test environment

• Root your device (App is now persistent, so it's Required) (adb root)
• Download artifact from latest pipeline
• Extract the release-unsigned APK
• Sign the APK accordingly to your test devices (apksigner sign --key xxx.pk8 --cert xxx.x509.pem --out eDrive.apk xxxx.apk)
• Manually push the signed APK on the device (adb remount then adb push eDrive.apk /system/app/eDrive/eDrive.apk)
• Reboot the device. (adb reboot)
• Register an /e/ account if no one is already registered.

example/help here

Test procedures

Check FileObserver start/stop with adb logcat | grep 'EdriveApplication*'

• Recursive File Observer must start to watch on:
  • first /e/ account registration
  • On device reboot if an account is registered
• RecursiveFileObserver must stop to watch on:
  • /e/ account deletion

EdriveApplication logcat example:

- waiting for device -
03-08 18:39:34.689  1996  1996 I EdriveApplication: Starting
03-08 18:39:34.745  1996  1996 D EdriveApplication: Account already registered
03-08 18:39:34.901  1996  1996 D EdriveApplication: Starting RecursiveFileObserver on media's root folder

check FileEvent is detected with adb logcat | grep 'FileEventListener*'

• DELETE when file/folder is deleted
• CLOSE_WRITE when file/folder is created/deleted/moved/edited

FileEvent logcat example:

03-08 18:18:42.301  2004  2209 D FileEventListener: CLOSE_WRITE event for :96.jpg
03-08 18:18:52.943  2004  2209 D FileEventListener: DELETE event for :96.jpg
03-08 18:18:52.962  2004  2209 D FileEventListener: DELETE event for :Screenshot_20220308-181736_Gallery.png
03-08 18:35:27.708  2004  2209 D FileEventListener: CLOSE_WRITE event for :Screenshot_20220308-183527_Gallery.png

⚠NO FILE TRANSFER due to FileObserver is expected from this MR ⚠

Technical details

Branch built over the one managed by MR !73 (merged) There was also a rebase, so code review can be started from 277bb13c

Screenshots

Check list

• Self review
• Test procedure explained
• Tested on fresh install
• Tested applied as an update
• License