[BUG][multiplatform] Test fails

Created by: tkirshboim

Bug Report Checklist

Have you provided a full/minimal spec to reproduce the issue?
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Description

The integration tests for Kotlin multiplatform fails.

openapi-generator version

Current master branch - commit: https://github.com/OpenAPITools/openapi-generator/commit/126e4061937fabd27a1ac020ca4dcfadb7b1e357

Steps to reproduce

Run the Kotlin multiplatform test by running the following command from the project's root folder:

./mvnw clean integration-test -f samples/client/petstore/kotlin-multiplatform/pom.xml

Expected: The test succeeds.

Actual: The test fails. See console output:

$ ./mvnw integration-test -f samples/client/petstore/kotlin-multiplatform/pom.xml 
[INFO] Scanning for projects...
[INFO] 
[INFO] -------< org.openapitools:kotlin-client-petstore-multiplatform >--------
[INFO] Building OpenAPI Petstore 1.0.0
[INFO] --------------------------------[ pom ]---------------------------------
[INFO] 
[INFO] --- maven-dependency-plugin:2.8:copy-dependencies (default) @ kotlin-client-petstore-multiplatform ---
[WARNING] The artifact xml-apis:xml-apis:jar:2.0.2 has been relocated to xml-apis:xml-apis:jar:1.0.b2
[INFO] 
[INFO] --- exec-maven-plugin:1.2.1:exec (bundle-test) @ kotlin-client-petstore-multiplatform ---

FAILURE: Build failed with an exception.

* Where:
Settings file './samples/client/petstore/kotlin-multiplatform/settings.gradle.kts' line: 1

* What went wrong:
There is no feature named GRADLE_METADATA

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 661ms
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  2.121 s
[INFO] Finished at: 2021-11-19T14:25:46+01:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.2.1:exec (bundle-test) on project kotlin-client-petstore-multiplatform: Command execution failed.: Process exited with an error: 1 (Exit value: 1) -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

Suggest a fix

The Gradle wrapper was upgraded to version 7.0.2 in #10468 but the obsolete GRADLE_METADATA Gradle feature preview flag was not removed from the template's settings.gradle file.

However, removing the obsolete GRADLE_METADATA is not sufficient to make the tests pass again. Upgrading Kotlin to version 1.5.31 together with upgrading the related dependencies is also necessary for the tests to pass.

I have a fix for this issue on a branch and I intend to create a PR for it. You can see the changes that I've done to resolve the issue here.