Improve Generation of the API Definition for API Products

[hisanhunais]

Purpose

• This PR adds the following improvements in the generation of the API definition for API products
  • Support for $ref reference within a Composed schema (allOf) in items of array schema
  • Support for $ref reference in header objects of responses

Approach

• Added the logic to process $ref reference within a Composed schemas in items of array schema
• Refactored the code segment of extracting references from composed schemas
• Added the logic to process $ref entries in header fields of response headers

Related Issues

• [APIM 4.1.0] Problems Arising from Nested Schemas in API Product Creation api-manager#3132
• [APIM 4.1.0] Issues with Referenced Response Header Schemas in API Product Creation api-manager#3304

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