Add deprecation constant.

Author: noordawod

modules/openapi-generator/src/main/resources/kotlin-client/libraries/jvm-retrofit2/infrastructure/ApiClient.kt.mustache

@@ -377,7 +377,13 @@ import okhttp3.MediaType.Companion.toMediaType
 
     {{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}companion object {
         @JvmStatic
-        protected val BASE_URL_KEY: String = "{{packageName}}.baseUrl"
+        protected const val BASE_URL_KEY: String = "{{packageName}}.baseUrl"
+        @Deprecated(
+          message = "Please use the capitalized constant `BASE_URL_KEY` instead.",
+          replaceWith = ReplaceWith("BASE_URL_KEY")
+        )
+        @JvmStatic
+        protected const val baseUrlKey: String = BASE_URL_KEY
 
         @JvmStatic
         {{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}val defaultBasePath: String by lazy {

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

@@ -13,7 +13,6 @@ import com.google.gson.reflect.TypeToken
 {{#nonPublicApi}}internal {{/nonPublicApi}}{{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}open class ApiClient(val basePath: kotlin.String = defaultBasePath, val accessToken: String? = null, val apiKey: MutableMap<String, String> = mutableMapOf(), val apiKeyPrefix: MutableMap<String, String> = mutableMapOf(), var username: String? = null, var password: String? = null, val vertx: Vertx) {
     {{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}companion object {
         {{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}const val BASE_URL_KEY: String = "{{packageName}}.baseUrl"
-
         @Deprecated(
           message = "Please use the capitalized constant `BASE_URL_KEY` instead.",
           replaceWith = ReplaceWith("BASE_URL_KEY")