Move RD settings from EE to CE

Issue: Move remote_development/settings to CE (#460515 - closed)

What does this MR do and why?

Moves RD settings from EE to CE

See Move remote_development/settings to CE (#460515 - closed) for detailed acceptance criteria and technical requirements.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

How to set up and validate locally

• Tests should be adequate to catch regressions, but if you wish you can test using the API described in https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/lib/remote_development/README.md#reading-settings
• For example: RemoteDevelopment::Settings.get_single_setting(:vscode_extensions_gallery_metadata, {user: User.find_by_username("root"), vscode_extensions_marketplace_feature_flag_enabled: false})