[kotlin][client] keep body on DELETE requests

Allow request body on DELETE in kotlin-client multiplatform and
jvm-ktor templates. RFC 9110 permits DELETE bodies; some APIs require
them (e.g. bulk-delete payloads). Mirrors the existing PUT/POST/PATCH
handling.

Author: walterbrebels

modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-ktor/infrastructure/ApiClient.kt.mustache

@@ -196,7 +196,7 @@ import {{packageName}}.auth.*
             }
             this.method = requestConfig.method.httpMethod
             headers.filter { header -> !UNSAFE_HEADERS.contains(header.key) }.forEach { header -> this.header(header.key, header.value) }
-            if (requestConfig.method in listOf(RequestMethod.PUT, RequestMethod.POST, RequestMethod.PATCH)) {
+            if (requestConfig.method in listOf(RequestMethod.PUT, RequestMethod.POST, RequestMethod.PATCH, RequestMethod.DELETE)) {
                 val contentType = (requestConfig.headers[HttpHeaders.ContentType]?.let { ContentType.parse(it) }
                     ?: ContentType.Application.Json)
                 this.contentType(contentType)

modules/openapi-generator/src/main/resources/kotlin-client/libraries/multiplatform/infrastructure/ApiClient.kt.mustache

@@ -166,7 +166,7 @@ import {{packageName}}.auth.*
             }
             this.method = requestConfig.method.httpMethod
             headers.filter { header -> !UNSAFE_HEADERS.contains(header.key) }.forEach { header -> this.header(header.key, header.value) }
-            if (requestConfig.method in listOf(RequestMethod.PUT, RequestMethod.POST, RequestMethod.PATCH)) {
+            if (requestConfig.method in listOf(RequestMethod.PUT, RequestMethod.POST, RequestMethod.PATCH, RequestMethod.DELETE)) {
                 val contentType = (requestConfig.headers[HttpHeaders.ContentType]?.let { ContentType.parse(it) }
                     ?: ContentType.Application.Json)
                 this.contentType(contentType)