Update Workspace configuration using API works incorrectly

[RomanNikitenko]

Bug Description:

I tried to update Workspace launch configurations using API and got incorrect JSON structure in workspace config file.
As result - updated launchconfigurations are not available for running from Debug panel.

You can see my code for testing here
So, I took launch section from workspace config and tried to update configurations section.

Expected:

"launch": {
            "configurations": [
                {
                    "name": "TEST: Attach to Chrome",
                    "port": 9222,
                    "request": "attach",
                    "type": "pwa-chrome",
                    "webRoot": ""
                }
            ]
        }

Actual:

"launch.configurations": [
            {
                "name": "TEST: Attach to Chrome",
                "port": 9222,
                "request": "attach",
                "type": "pwa-chrome",
                "webRoot": ""
            }
        ]

Steps to Reproduce:

1. Clone my test vs code extension: https://github.com/RomanNikitenko/vscode-test-extension.git
2. Build it and copy to plugins folder of the theia
3. Open a multi-root workspace from a config file for testing.
4. F1 => Test: Update Workspace launch configurations

The command should:

• add new test Workspace-scoped launch configuration to workspace config file if there is no configurations defined
• replace existed Workspace-scoped launch configurations by test launch config if there is at least one configuration defined in workspace config file

The new test configuration should be available for running from Debug panel.
But it isn't, as at the moment there is the described bug in theia.

Additional Information

• Operating System: Fedora 31
• Theia Version: 4204297