[BUG][Typescript fetch] JSON-serialization does not obay timezone for date fields

Created by: stephanpelikan

Description

I'm located in Austria which is GMT+1 and in daylight-saving period it is GMT+2. When I have this API definition

openapi: 3.0.0
...
components:
  schemas:
    MemberApplicationForm:
      type: object
      properties:
        birthdate:
          type: string
          format: date

and set a Javascript Date new Date('2022-06-05T00:00:00') then the toISOString() method returns 2022-06-04T22:00:00.000Z which is used as a bases for date formatting in JSON. Therefore the date is '2022-06-04' instead of '2022-06-05'!

Files affected:

1. modules/openapi-generator/src/main/resources/typescript-fetch/apis.mustache
2. modules/openapi-generator/src/main/resources/typescript-fetch/modelGeneric.mustache

openapi-generator version

6.0.0

OpenAPI declaration file content or url

Generation Details

Maven build:

			<plugin>
				<groupId>org.openapitools</groupId>
				<artifactId>openapi-generator-maven-plugin</artifactId>
				<version>6.0.0</version>
				<executions>
					<execution>
						<id>generate-administration-api</id>
						<goals>
							<goal>generate</goal>
						</goals>
						<configuration>
							<inputSpec>${project.basedir}/src/main/resources/api/administration/v1.yaml</inputSpec>
							<output>${project.build.directory}/generated-sources</output>
							<generatorName>spring</generatorName>
							<apiPackage>at.demo.administration.api.v1</apiPackage>
							<modelPackage>at.demo.administration.api.v1</modelPackage>
							<generateSupportingFiles>true</generateSupportingFiles>
							<supportingFilesToGenerate>ApiUtil.java</supportingFilesToGenerate>
							<configOptions>
								<sourceFolder>openapi</sourceFolder>
								<interfaceOnly>true</interfaceOnly>
								<useSpringController>true</useSpringController>
								<dateLibrary>java8</dateLibrary>
								<useBeanValidation>true</useBeanValidation>
							</configOptions>
							<addCompileSourceRoot>true</addCompileSourceRoot>
						</configuration>
					</execution>
				</executions>
			</plugin>

Steps to reproduce

See description

Related issues/PRs

This PR also belongs to date/time in Typescript fetch but does not fix that issue: https://github.com/OpenAPITools/openapi-generator/pull/11685/commits/2cde020568701b92b3a347d26fc8e746c172bbb0#

Suggest a fix

const offset = yourDate.getTimezoneOffset()
yourDate = new Date(yourDate.getTime() - (offset*60*1000))
return yourDate.toISOString().substr(0,10);