launsh.json增加cppdbg (oceanbase#280)

### What problem were solved in this pull request?

Problem:
lldb 调试配置不能在某些linux平台中运行

### What is changed and how it works?
增加cppdbg和lldb两种调试配置

Author: hnwyllmm

.vscode/launch.json

@@ -5,11 +5,23 @@
     "version": "0.2.0",
     "configurations": [
         {
-            "type": "lldb",
+            "type": "cppdbg",
             "request": "launch",
             "name": "Debug",
             "program": "${workspaceFolder}/${defaultBuildTask}/bin/observer",
             "args": ["-f", "${workspaceFolder}/etc/observer.ini", "-P", "cli"],
+            "cwd": "${workspaceFolder}/${defaultBuildTask}/",
+            "stopAtEntry": true,
+            "osx": {
+                "MIMode": "lldb"
+            }
+        },
+        {
+            "type": "lldb",
+            "request": "launch",
+            "name": "LLDB",
+            "program": "${workspaceFolder}/${defaultBuildTask}/bin/observer",
+            "args": ["-f", "${workspaceFolder}/etc/observer.ini", "-P", "cli"],
             "cwd": "${workspaceFolder}/${defaultBuildTask}/"
         }
     ]

docs/src/dev-env/miniob-how-to-debug.md

@@ -224,4 +224,8 @@ LOG_CONSOLE_LEVEL=1
     Quit anyway? (y or n) y
     Detaching from program: /home/caizj/local/bin/observer, process 54699
     [Inferior 1 (process 54699) detached]
-    ```
+    ```
+
+### Visual Studio Code 调试
+代码中已经为vscode配置了launch.json，可以直接启动调试。
+launch.json中有两个调试配置，一个是Debug，一个是LLDB。其中Debug使用cppdbg，会自动探测调试工具gdb或lldb，而LLDB会使用lldb调试工具。通常情况下，大家使用Debug就可以了，但是我在测试过程中发现cppdbg不能在macos上正常工作，因而增加了LLDB的配置，以便在macos上调试，如果使用macos的同学，可以使用LLDB配置启动调试程序。