Add Grok/XAI support for LLM & agents (#2517)

.vscode/settings.json

docker/.env.example

frontend/src/components/LLMSelection/XAiLLMOptions/index.jsx

frontend/src/hooks/useGetProvidersModels.js

frontend/src/media/llmprovider/xai.png

frontend/src/pages/GeneralSettings/LLMPreference/index.jsx

...end/src/pages/OnboardingFlow/Steps/DataHandling/index.jsx

...nd/src/pages/OnboardingFlow/Steps/LLMPreference/index.jsx

...WorkspaceSettings/AgentConfig/AgentLLMSelection/index.jsx

server/.env.example

server/models/systemSettings.js

server/utils/AiProviders/modelMap.js

server/utils/AiProviders/xai/index.js

server/utils/agents/aibitat/index.js

server/utils/agents/aibitat/providers/ai-provider.js

server/utils/agents/aibitat/providers/index.js

server/utils/agents/aibitat/providers/xai.js

server/utils/agents/index.js

server/utils/helpers/customModels.js

server/utils/helpers/index.js