feat(Core/Config): Implement config override with env vars (#16817)

* Core/Config: Implement config override with env vars

Implement overriding of configuration from the .conf file with environment variables.
Environment variables keys are autogenerated based on the keys defined in .conf file.

Usage example:

$ export TC_DATA_DIR=/usr
$ AC_WORLD_SERVER_PORT=8080 ./worldserver

* Add tests for env vars config

src/test/common/Configuration/Config.cpp

@@ -0,0 +1,124 @@
+/*
+ * This file is part of the AzerothCore Project. See AUTHORS file for Copyright information
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Affero General Public License as published by the
+ * Free Software Foundation; either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "Config.h"
+#include "gtest/gtest.h"
+
+#include <boost/filesystem.hpp>
+#include <cstdlib>
+#include <string>
+
+std::string CreateConfigWithMap(std::map<std::string, std::string> const& map)
+{
+    auto mTempFileRel = boost::filesystem::unique_path("deleteme.ini");
+    auto mTempFileAbs = boost::filesystem::temp_directory_path() / mTempFileRel;
+    std::ofstream iniStream;
+    iniStream.open(mTempFileAbs.c_str());
+
+    iniStream << "[test]\n";
+    for (auto const& itr : map)
+        iniStream << itr.first << " = " << itr.second << "\n";
+
+    iniStream.close();
+
+    return mTempFileAbs.native();
+}
+
+class ConfigEnvTest : public testing::Test {
+protected:
+    void SetUp() override {
+        std::map<std::string, std::string> config;
+        config["Int.Nested"] = "4242";
+        config["lower"] = "simpleString";
+        config["UPPER"] = "simpleString";
+        config["SomeLong.NestedNameWithNumber.Like1"] = "1";
+        config["GM.InGMList.Level"] = "50";
+
+        confFilePath = CreateConfigWithMap(config);
+
+        sConfigMgr->Configure(confFilePath, std::vector<std::string>());
+        sConfigMgr->LoadAppConfigs();
+    }
+
+    void TearDown() override {
+        std::remove(confFilePath.c_str());
+    }
+
+    std::string confFilePath;
+};
+
+TEST_F(ConfigEnvTest, NestedInt)
+{
+    EXPECT_EQ(sConfigMgr->GetOption<int32>("Int.Nested", 10), 4242);
+    setenv("AC_INT_NESTED", "8080", 1);
+    EXPECT_EQ(sConfigMgr->OverrideWithEnvVariablesIfAny().empty(), false);
+    EXPECT_EQ(sConfigMgr->GetOption<int32>("Int.Nested", 10), 8080);
+}
+
+TEST_F(ConfigEnvTest, SimpleLowerString)
+{
+    EXPECT_EQ(sConfigMgr->GetOption<std::string>("lower", ""), "simpleString");
+    setenv("AC_LOWER", "envstring", 1);
+    EXPECT_EQ(sConfigMgr->OverrideWithEnvVariablesIfAny().empty(), false);
+    EXPECT_EQ(sConfigMgr->GetOption<std::string>("lower", ""), "envstring");
+}
+
+TEST_F(ConfigEnvTest, SimpleUpperString)
+{
+    EXPECT_EQ(sConfigMgr->GetOption<std::string>("UPPER", ""), "simpleString");
+    setenv("AC_UPPER", "envupperstring", 1);
+    EXPECT_EQ(sConfigMgr->OverrideWithEnvVariablesIfAny().empty(), false);
+    EXPECT_EQ(sConfigMgr->GetOption<std::string>("UPPER", ""), "envupperstring");
+}
+
+TEST_F(ConfigEnvTest, LongNestedNameWithNumber)
+{
+    EXPECT_EQ(sConfigMgr->GetOption<float>("SomeLong.NestedNameWithNumber.Like1", 0), 1);
+    setenv("AC_SOME_LONG_NESTED_NAME_WITH_NUMBER_LIKE_1", "42", 1);
+    EXPECT_EQ(sConfigMgr->OverrideWithEnvVariablesIfAny().empty(), false);
+    EXPECT_EQ(sConfigMgr->GetOption<float>("SomeLong.NestedNameWithNumber.Like1", 0), 42);
+}
+
+TEST_F(ConfigEnvTest, ValueWithSeveralUpperlLaters)
+{
+    EXPECT_EQ(sConfigMgr->GetOption<int>("GM.InGMList.Level", 1), 50);
+    setenv("AC_GM_IN_GMLIST_LEVEL", "42", 1);
+    EXPECT_EQ(sConfigMgr->OverrideWithEnvVariablesIfAny().empty(), false);
+    EXPECT_EQ(sConfigMgr->GetOption<int>("GM.InGMList.Level", 0), 42);
+}
+
+TEST_F(ConfigEnvTest, StringThatNotExistInConfig)
+{
+    setenv("AC_UNIQUE_STRING", "somevalue", 1);
+    EXPECT_EQ(sConfigMgr->GetOption<std::string>("Unique.String", ""), "somevalue");
+}
+
+TEST_F(ConfigEnvTest, IntThatNotExistInConfig)
+{
+    setenv("AC_UNIQUE_INT", "100", 1);
+    EXPECT_EQ(sConfigMgr->GetOption<int>("Unique.Int", 1), 100);
+}
+
+TEST_F(ConfigEnvTest, NotExistingString)
+{
+    EXPECT_EQ(sConfigMgr->GetOption<std::string>("NotFound.String", "none"), "none");
+}
+
+TEST_F(ConfigEnvTest, NotExistingInt)
+{
+    EXPECT_EQ(sConfigMgr->GetOption<int>("NotFound.Int", 1), 1);
+}