Heavy background jobs of other apps pause while a backup runs

Reserved in Nextcloud's job list, so no app is turned off and a job that is running goes on.
At most 6 hours in a row, then they get an hour; Nextcloud ends a reservation by itself after
12 hours, should the end of a pause never come. On by default, with a setting to turn it off.

README.md

@@ -336,6 +336,7 @@ On the backlog; know them before you rely on NG Backup:
 | `backup:browse`, `backup:restore` | browse and restore |
 | `backup:retention`, `backup:prune`, `backup:trash`, `backup:trash:restore` | retention, cleanup, trash |
 | `backup:pin`, `backup:note` | keep a restore point, a note you can change later |
+| `backup:pause-jobs` | whether heavy background jobs of other apps pause during a backup |
 | `backup:verify` | checksum audit of a restore point (`--deep` downloads and decrypts everything) |
 | `backup:restore:full` | whole-server restore onto a fresh installation (after `backup:key:import`) |
 | `backup:key:import` | import a recovery kit on a fresh installation |