[BUG][JAVA] defaultValue not set for @RequestHeader in generated spring api file

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When generating spring api interfaces the query parameters with a default value assigned behave as I expect:

• defaultValue in @ApiParam is set
• defaultValue in @RequestParam is set

However the situation looks different for header parameters with a default value:

• defaultValue in @ApiParam is set
• defaultValue in @RequestHeader is NOT set

I would expect that defaultValue is also set in @RequestHeader.

openapi-generator version

master

OpenAPI declaration file content or url

This file:
https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/JavaSpring/headerParams.mustache
does not contain the defaultValue entries like specified here:
https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/JavaSpring/queryParams.mustache

Generation Details

See below

Steps to reproduce

See sample codes here:
https://github.com/OpenAPITools/openapi-generator/blob/master/samples/server/petstore/spring-mvc-default-value/src/main/resources/openapi.yaml
https://github.com/OpenAPITools/openapi-generator/blob/master/samples/server/petstore/spring-mvc-default-value/src/main/java/org/openapitools/api/TestHeadersApi.java
https://github.com/OpenAPITools/openapi-generator/blob/master/samples/server/petstore/spring-mvc-default-value/src/main/java/org/openapitools/api/TestQueryParamsApi.java

Related issues/PRs

None so far

Suggest a fix

See linked mustache files above

Start by comparing modules/openapi-generator/src/main/resources/JavaSpring/headerParams.mustache with queryParams.mustache, then inspect the spring-mvc-default-value sample files listed in the issue. Done means generated Spring API header parameters include the expected defaultValue behavior, matching the query parameter example.