Browser locale language support in Kibana

**What the feature is**
Browser Locale Language allows users to view the Kibana interface in their preferred language (French, German, Japanese, Chinese, or English) by automatically detecting and applying the setting configured in their web browser, without having to configure a .yml file.

**Value Proposition**
Currently, global organizations are forced to default all users to English, despite having employees across multiple countries and languages. Users on Serverless cannot change their language setting. This creates a significant usability gap and makes Kibana less accessible and less competitive compared to multi-language competitors like Grafana and Splunk. By automatically detecting the browser locale, Kibana offers a personalized experience that improves adoption may make it easier for some customers to migrate from on-premises to Elastic Cloud and Serverless.

**Expected Outcome**
- Kibana will automatically detect the user's browser-set preferred language on first load and apply the corresponding language (e.g., zh-CN, ja-JP, fr-FR).
- Users can override the language setting with a UI control
- For on-premise users, this UI setting will override the default language set in kibana.yml, enabling multi-language support even within a single on-prem deployment.

**Key User Stories / Use Cases**
User Story: "As a Japanese Analyst on Serverless, I want Kibana to automatically appear in Japanese when I log in, without having to ask my administrator to change a server configuration file I don't have access to."
User Story: "As a Global Administrator of an ECH deployment, I want users in Germany and France to be able to use Kibana in their respective languages without me having to manage separate deployment instances."