Add policy to change response (body, header, statuscode) based on context (e.g. backend response code)

[davihern]

Some policy similar to:

    <choose>
        <when condition="@(context.Response.StatusCode == 500)">
            <return-response>
                <set-status code="510" reason="Internal APIM error captured" />
                <set-header name="CustomHeader" exists-action="override">
                    <value>Error captured and sanitized by APIM</value>
                </set-header>

@{
var response = context.Response.Body.As();

    return Regex.Replace(response, "A", "*");
  }</set-body>
            </return-response>
        </when>
    </choose>
    <find-and-replace from="SECRET" to="*S*" />