adding templates for launch.json in VSCode

[JojoS62]

mbed-ce generates the file .vscode/launch.json with debug configurations. This is done in cmake code by writing the content line by line.
But there is a more conveniant way in cmake by using template files. CMake can replace special marked placeholders like @SERVER_TYPE@ by cmake variables. So this makes it easier to supply additional debug configurations, as the internal servers in cortex-debug work better than the external + openOCD configuration.
An example is in the cmake tutorial:
https://github.com/Kitware/CMake/tree/master/Help/guide/tutorial/Step2

I've tested this with a config.json.in and it will create a config.json with:

set(REQUEST_TYPE "attach")
set(SERVER_TYPE "stlink")

configure_file(Config.json.in Config.json)

Config.json.in (not complete):

{
    "configurations": [
        {
               "type": "cortex-debug",
               "name": "Connect to GDB app_hello DISCO_F746NG Debug",
                "executable": "./build/app_Hello/app_hello.elf",
                "servertype": "@SERVER_TYPE@",
                "request": "@REQUEST_TYPE@"
        },

This will make it easier to add additional settings, e.g. you need to a serial no. for the debug probe when more than one is connected to the PC.