Add custom attributes to extensions management API

[asha15]

Purpose

$subject

currently the template listing API (api/server/v1/extensions) has a strict schema, from this PR we're doing the improvement to add metadata about the template. we can add the additional information as custom attributes in info.json file.

The improvement will support the below structure:

{
"id": "mobile-application",
    "name": "Mobile Application",
    "description": "Applications developed to target mobile devices.",
    "image": "abc.jpg",
    "category": "DEFAULT",
    "displayOrder": 4,
    "tags": [ "android" ],
    "type": "applications",
    "customAttributes":  [
            {
                "key": "publisher",
                "value": {
                    "displayName": "vendor",
                    "logo": "XYZ"
                }
            },
            {
                "key": "supportedTechnologies",
                "value": [
                    {
                        "displayName": "Flutter",
                        "logo": "https://www.svgrepo.com/show/353751/flutter.svg"
                    },
                    {
                        "displayName": "Android",
                        "logo": "https://upload.wikimedia.org/wikipedia/commons/thumb/d/d7/Android_robot.svg/1745px-Android_robot.svg.png"
                    },
                    {
                        "displayName": "Swift",
                        "logo": "https://i.pinimg.com/originals/8f/50/63/8f50630ae0e1775196e4c270c573ce67.png"
                    },
                    {
                        "displayName": "React Native",
                        "logo": "https://www.datocms-assets.com/45470/1631026680-logo-react-native.png"
                    },
                    {
                        "displayName": "Iconic",
                        "logo": "https://images.prismic.io/ionicframeworkcom/66cfdbef-e59d-463a-8e24-12cb233e9d97_ionic+logo+blue.png?auto=compress,format"
                    }
                ]
            }
        ]
}

Related issue: wso2/product-is#16745

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PR builder started
Link: https://github.com/wso2/product-is/actions/runs/6610017882

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Link: https://github.com/wso2/product-is/actions/runs/6610017882
Status: success

[jenkins-is-staging]

Approving the pull request based on the successful pr build https://github.com/wso2/product-is/actions/runs/6610017882