Enhance Metrics Reporter Policy documentation with EL samples (Logging of Arrays)

[apoddany]

Add some samples on how to log for example the Headers or Params of the Request.

One example to log the Request Headers in multiple ways :

{
    "requestId": "${request.id}",
    "transactionId": "${request.transactionId}",
    "requestHeaders": [
        "${request.headers['User-Agent'][0]}"
    ],
    "requestHeadersList": {
    <#list request.headers as header, value>
    "${header}": "${value?join(",
        ")}"<#sep>,
    </#list>
    },
    "requestHeadersList2": {
    <#list request.headers as header, values>
    "${header}": [
    <#list values as value>
    "${value}"<#sep>,
    </#list>
        ]<#sep>,
    </#list>
    },
    "requestMethod": "${request.method}",
    "uri": "${request.uri}",
    "path": "${request.path}",
    "planUsed": "${request.metrics.plan}"
}

this will result in the following output :

{
    "requestId": "589be0b2-4350-4d08-9be0-b243507d08a1",
    "transactionId": "589be0b2-4350-4d08-9be0-b243507d08a1",
    "requestHeaders": [
        "PostmanRuntime/7.28.4"
    ],
    "requestHeadersList": {
        "X-Forwarded-For": "12.34.56.78",
        "X-Forwarded-Proto": "https",
        "X-Forwarded-Port": "443",
        "Host": "api-dev.graviteeio.com",
        "X-Amzn-Trace-Id": "Root=1-615eead9-6d6e2ae5047bbca1301d6c59",
        "test": "test,123,456, sdfsdf",
        "User-Agent": "PostmanRuntime/7.28.4",
        "Accept": "*/*",
        "Postman-Token": "295d04d0-1a6e-4ef9-838d-271b5213ecb1",
        "Accept-Encoding": "gzip, deflate, br",
        "X-Gravitee-Transaction-Id": "589be0b2-4350-4d08-9be0-b243507d08a1",
        "X-Gravitee-Request-Id": "589be0b2-4350-4d08-9be0-b243507d08a1"
    },
    "requestHeadersList2": {
        "X-Forwarded-For": [
            "12.34.56.78"
        ],
        "X-Forwarded-Proto": [
            "https"
        ],
        "X-Forwarded-Port": [
            "443"
        ],
        "Host": [
            "api-dev.graviteeio.com"
        ],
        "X-Amzn-Trace-Id": [
            "Root=1-615eead9-6d6e2ae5047bbca1301d6c59"
        ],
        "test": [
            "test,123,456",
            "sdfsdf"
        ],
        "User-Agent": [
            "PostmanRuntime/7.28.4"
        ],
        "Accept": [
            "*/*"
        ],
        "Postman-Token": [
            "295d04d0-1a6e-4ef9-838d-271b5213ecb1"
        ],
        "Accept-Encoding": [
            "gzip, deflate, br"
        ],
        "X-Gravitee-Transaction-Id": [
            "589be0b2-4350-4d08-9be0-b243507d08a1"
        ],
        "X-Gravitee-Request-Id": [
            "589be0b2-4350-4d08-9be0-b243507d08a1"
        ]
    },
    "requestMethod": "GET",
    "uri": "/at/echo",
    "path": "/at/echo",
    "planUsed": "78033416-dce4-493a-8334-16dce4c93ada"
}