core: add quota support for State, Cache, and Log exec directories

docs/DISK-QUOTAS-PROJECTIDS.md

@@ -0,0 +1,14 @@
+---
+title: Project IDs for Disk Quotas on Exec Directories
+category: Exec directories
+layout: default
+SPDX-License-Identifier: LGPL-2.1-or-later
+---
+
+# Project IDs on systemd Systems
+
+Project IDs are needed to enforce disk quotas for Exec Directories.
+Project IDs are unsigned, 32-bit integers. For disk quota enforcement,
+the range used is 2147483648 - 4294967294, which is the highest range
+inspired from `UIDS-GUID.md`. The range is defined through `PROJ_ID_MIN`
+and `PROJ_ID_MAX` in `exec-invoke.c`.

docs/TRANSIENT-SETTINGS.md

@@ -257,10 +257,16 @@ All execution-related settings are available for transient units.
 ✓ RuntimeDirectoryMode=
 ✓ RuntimeDirectory=
 ✓ StateDirectoryMode=
+✓ StateDirectoryAccounting=
+✓ StateDirectoryQuota=
 ✓ StateDirectory=
 ✓ CacheDirectoryMode=
+✓ CacheDirectoryAccounting=
+✓ CacheDirectoryQuota=
 ✓ CacheDirectory=
 ✓ LogsDirectoryMode=
+✓ LogsDirectoryAccounting=
+✓ LogsDirectoryQuota=
 ✓ LogsDirectory=
 ✓ ConfigurationDirectoryMode=
 ✓ ConfigurationDirectory=