config: Enable printing a whole group or domain

This is done by calling `config DOMAIN_TO_PRINT` or `config DOMAIN
GROUP_TO_PRINT`.

Base/usr/share/man/man1/config.md

@@ -5,7 +5,7 @@ config
 ## Synopsis
 
 ```sh
-$ config [--remove] <domain> <group> [key] [value]
+$ config [--remove] <domain> [group] [key] [value]
 ```
 
 ## Description

Userland/Utilities/config.cpp

@@ -4,11 +4,25 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include <AK/QuickSort.h>
 #include <LibConfig/Client.h>
 #include <LibCore/ArgsParser.h>
 #include <LibCore/EventLoop.h>
 #include <LibMain/Main.h>
 
+static void print_group(StringView domain, StringView group)
+{
+    auto keys = Config::Client::the().list_keys(domain, group);
+    quick_sort(keys);
+    for (auto const& key : keys) {
+        auto value = Config::Client::the().read_string_value(domain, group, key);
+        if (!value.has_value())
+            warnln("Can't find a value for {}:{}:{}", domain, group, key);
+        else
+            outln("{}={}", key, *value);
+    }
+}
+
 ErrorOr<int> serenity_main(Main::Arguments arguments)
 {
     Core::EventLoop loop;
@@ -22,24 +36,42 @@ ErrorOr<int> serenity_main(Main::Arguments arguments)
     args_parser.set_general_help("Show or modify values in the configuration files through ConfigServer.");
     args_parser.add_option(remove, "Remove group or key", "remove", 'r');
     args_parser.add_positional_argument(domain, "Config domain", "domain");
-    args_parser.add_positional_argument(group, "Group name", "group");
+    args_parser.add_positional_argument(group, "Group name", "group", Core::ArgsParser::Required::No);
     args_parser.add_positional_argument(key, "Key name", "key", Core::ArgsParser::Required::No);
     args_parser.add_positional_argument(value_to_write, "Value to write", "value", Core::ArgsParser::Required::No);
     args_parser.parse(arguments);
 
     if (remove) {
-        if (!key.is_empty())
-            Config::remove_key(domain, group, key);
-        else
+        if (group.is_empty())
+            return Error::from_string_literal("Can't delete a domain");
+        if (key.is_empty())
             Config::remove_group(domain, group);
+        else
+            Config::remove_key(domain, group, key);
         return 0;
     }
 
-    if (!key.is_empty() && !value_to_write.is_empty()) {
+    if (!group.is_empty() && !key.is_empty() && !value_to_write.is_empty()) {
         Config::write_string(domain, group, key, value_to_write);
         return 0;
     }
 
+    if (group.is_empty()) {
+        auto groups = Config::Client::the().list_groups(domain);
+        quick_sort(groups);
+
+        for (auto const& group : groups) {
+            outln("[{}]", group);
+            print_group(domain, group);
+        }
+        return 0;
+    }
+
+    if (key.is_empty()) {
+        print_group(domain, group);
+        return 0;
+    }
+
     auto value_or_error = Config::Client::the().read_string_value(domain, group, key);
     if (!value_or_error.has_value())
         return 1;