Add 'View Plugins' global capability that allows to list plugins

At the moment only the Gerrit administrators can list the installed
plugins. However which plugins are installed may be also interesting
to project owners and users because they want to know which
functionality is available to them. Hiding the 'Plugins' > 'Installed'
menu is bad since this screen is the entry point to the documentation
of the installed plugins. This documentation may be relevant to normal
users.

Since being able to see the list of installed plugin may be considered
as security risk, by default still only administrators are able to
list them, but now the new capability allows to assign this permission
also to other users.

Change-Id: Ifed8ad76354b9a19e8c79edb0c965249b162fdfd
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
diff --git a/Documentation/access-control.txt b/Documentation/access-control.txt
index 8b2fd64..8ff2eb6 100644
--- a/Documentation/access-control.txt
+++ b/Documentation/access-control.txt
@@ -1311,6 +1311,12 @@
 link:cmd-show-connections.html[look at Gerrit's current connections via ssh].
 
 
+[[capability_viewPlugins]]
+=== View Plugins
+
+Allow viewing the list of installed plugins.
+
+
 [[capability_viewQueue]]
 === View Queue