[Improvement]: Fix deprecation inside default devcontainer

[Shadow-Devil]

Description

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Change the default template to this:

{
    "image": "ballerina/ballerina-devcontainer:latest",
    "customizations":{
        "vscode": {
            "extensions": ["WSO2.ballerina"]
        }
    }
}

Related area

-> Other Area

Related issue(s) (optional)

#32546

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I would like to contribute myself