Add support for resources with mock implementations in API Products

[ashanhr]

Purpose

• Currently, API Products do not support resources with mock implementations. To enable this functionality, it is necessary to check for the availability of the mediation script in the api_product_template.xml.
• Resolves: Mock endpoints not working when used in API products api-manager#3436

Approach

• Syncing Mediation Scripts: The mediation script of the original API resource is not currently synced with the corresponding product resource (only when the original API endpoint type is INLINE). This has been fixed to ensure that mediation scripts are properly synced and can be accessed within the api_product_template.xml.
• Fixing Mediation Script Setting During Aggregation: Mediation scripts were not being set properly when aggregating resources based on the resource key. This issue has also been resolved in this PR.