fix(clients): correct user agent

Author: millotp

clients/algoliasearch-client-dart/packages/client_core/lib/src/transport/dio/platform/platform_web.dart

@@ -13,5 +13,5 @@ Iterable<AgentSegment> platformAgentSegments() => [
 
 /// [AlgoliaAgent] for web platforms as query param.
 void platformAlgoliaAgent(dio.RequestOptions options, String agent) {
-  options.queryParameters["X-Algolia-Agent"] = agent;
+  options.queryParameters["x-algolia-agent"] = agent;
 }

clients/algoliasearch-client-swift/Sources/Core/Networking/RequestBuilder/EchoRequestBuilder.swift

@@ -78,7 +78,7 @@ final class EchoRequestBuilder: RequestBuilder {
             originalBodyData: urlRequest.httpBody,
             path: urlComponents?.percentEncodedPath ?? "",
             host: url.host ?? "",
-            algoliaAgent: headers["X-Algolia-Agent"] ?? "",
+            algoliaAgent: headers["user-agent"] ?? "",
             queryParameters: queryParameters,
             headers: headers
         )

website/docs/add-new-language.md

@@ -110,7 +110,7 @@ The `User-Agent` MUST match the following regular expression:
 ^Algolia for <LANGUAGE> \\(\\d+\\.\\d+\\.\\d+(-?.*)?\\)(; [a-zA-Z. ]+ (\\(\\d+((\\.\\d+)?\\.\\d+)?(-?.*)?\\))?)*(; <CLIENT> (\\(\\d+\\.\\d+\\.\\d+(-?.*)?\\)))(; [a-zA-Z. ]+ (\\(\\d+((\\.\\d+)?\\.\\d+)?(-?.*)?\\))?)*$
 ```
 
-The function MUST be named `addAlgoliaAgent` because of JavaScript exception that doesn't allow custom `User-Agent` in the header, and must use `x-algolia-agent` for JavaScript.
+The function MUST be named `addAlgoliaAgent` because of JavaScript exception that doesn't allow custom `User-Agent` in the header, and must use `x-algolia-agent` for JavaScript and Dart.
 
 ### Dependencies