Add content type for set personalisation strategy request

Author: VladislavFitz

Sources/AlgoliaSearchClient/Command/Command+Personalization.swift

@@ -31,6 +31,8 @@ extension Command {
       let requestOptions: RequestOptions?
 
       init(strategy: PersonalizationStrategy, requestOptions: RequestOptions?) {
+        var requestOptions = requestOptions.unwrapOrCreate()
+        requestOptions.setHeader("application/json", forKey: .contentType)
         self.requestOptions = requestOptions
         self.urlRequest = .init(method: .post, path: .strategies >>> PersonalizationRoute.personalization, body: strategy.httpBody, requestOptions: self.requestOptions)
       }