Add cloud connector base url

What does this MR do and why?

in gitlab-com/gl-infra/production-engineering#24711 (comment 1685184021) we introduced Cloudflare load balancer for cloud connector

• https://cloud.gitlab.com/ai goes to the Code Suggestions service in gprd

This MR introduces Gitlab.config.cloud_connector.base_url pointing to https://cloud.gitlab.com It also uses use_cloud_connector_lb feature flag to send requests to https://cloud.gitlab.com/ai instead of codesuggestions.gitlab.com

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