mod_admin_shell: Make 'Role' column dynamically sized

Some of the new roles don't quite fit nicely into 4 characters
(excluding ellipsis). Given the ability to dynamically add additional
roles from the config and possibly from modules, it seems better to just
make it a relative size since we can't know how long they will be.

plugins/mod_admin_shell.lua

@@ -1018,7 +1018,7 @@ available_columns = {
 	role = {
 		title = "Role";
 		description = "Session role with 'prosody:' prefix removed";
-		width = #"admin";
+		width = "1p";
 		key = "role";
 		mapper = function(role)
 			local name = role and role.name;