feat: Add extensionsGallerySettings to config

Issue: Update Web IDE to receive `extensionMarketplace... (#322 - closed)

Dependent MR: feat: Update extensions view gl_mod with extens... (gitlab-web-ide-vscode-fork!78 - merged)

Description

• Updates VSCode version
• Adds checkbox to Example app
• We need to make sure we load crossOriginExtensionHost if this setting is available.

Screenshots

Please note! The UI text has been updated after the Technical Writing review. The functionality is the same though.

Extension Marketplace enabled	Extension Marketplace disabled (no reason)	Extension Marketplace instance_disabled	Extension Marketplace opt_in_unset

Screen_Recording_2024-04-29_at_6.50.21_AM

How to test

Extensions Marketplace Enabled

1. Start the Web IDE Example App and check Enabled Extensions Marketplace.
2. Fill in the other information as usual and hit Start GitLab Web IDE.
3. The extensions marketplace should work and you should be able to install extensions 🎉.

Extensions Marketplace Disabled

1. Start the Web IDE Example App and uncheck Enabled Extensions Marketplace.
2. Fill in the other information as usual and hit Start GitLab Web IDE.
3. The extensions marketplace should be disabled and a friendly message displayed in the extensions view.

Extensions Marketplace Disabled with reason `instance_disabled`

1. Start the Web IDE Example App and add ?extensionsGalleryReason=instance_disabled and uncheck Enabled Extensions Marketplace.
2. Fill in the other information as usual and hit Start GitLab Web IDE.
3. The extensions marketplace should be disabled and a friendly message with Learn More displayed in the extensions view.
4. The Learn More link should open some documentation when clicked (this will be more accurately configured in the main project).

Extensions Marketplace Disabled with reason `opt_in_unset`

1. Start the Web IDE Example App and add ?extensionsGalleryReason=opt_in_unset and uncheck Enabled Extensions Marketplace.
2. Fill in the other information as usual and hit Start GitLab Web IDE.
3. The extensions marketplace should be disabled and a friendly message displayed in the extensions view.
4. The Learn More link should open some documentation when clicked (this will be more accurately configured in the main project).
5. The Open user preferences button should open the current user's preferences in a separate tab.

Known issues

• When the extensions marketplace is disabled, we take over the "Installed" view, but user's could have had this view unchecked, so they will miss our message.
• [UX Investigation] When user has extensions ins... (#335)