Update config on change, add revealIfOpen to contributes

[UliPlabst]

• Add a subscription to update the extension configuration on change.
• Expose the setting revealIfOpen (previously named reuseView) in contributes (package.json) to make it available (the setting was present the implementation but missing in contributes)
• Rename reuseView setting to revealIfOpen setting to use the same settingsname that vscode uses internally