Add user and group for System-proxy daemon

Adds a user and group for a new system daemon that acts as an
unauthenticated proxy on Chrome OS. This daemon will authenticate and
set up a connection for system services, ARC apps and Linux utilities
that are proxy aware, but can't perform the authentication challenge
themselves.

BUG=chromium:1041780
TEST=Emerges

Cq-Depend: chromium:2000174, chromium:2000877
Change-Id: I8cd7ca553c665611f7980914b5fc834e3cffb87b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/overlays/eclass-overlay/+/2000897
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Hugo Benichi <hugobenichi@google.com>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Tested-by: Andreea-Elena Costinas <acostinas@google.com>
Commit-Queue: Andreea-Elena Costinas <acostinas@google.com>
diff --git a/profiles/base/accounts/group/system-proxy b/profiles/base/accounts/group/system-proxy
new file mode 100644
index 0000000..b622025
--- /dev/null
+++ b/profiles/base/accounts/group/system-proxy
@@ -0,0 +1,3 @@
+group:system-proxy
+gid:20154
+users:system-proxy
diff --git a/profiles/base/accounts/user/system-proxy b/profiles/base/accounts/user/system-proxy
new file mode 100644
index 0000000..96be27a
--- /dev/null
+++ b/profiles/base/accounts/user/system-proxy
@@ -0,0 +1,6 @@
+user:system-proxy
+uid:20154
+gid:20154
+gecos:CrOS System-wide proxy daemon
+home:/dev/null
+shell:/bin/false