Add marketing tab for VNet in Connect

[ravicious]

Initial mockup of the tab

The tab should explain what VNet is and why you would use it.

It should allow the user to start VNet, where starting VNet should open the VNet panel and then start VNet. The VNet panel is the only place in the UI where we show errors related to VNet startup.

When the user clicks on "Connect" next to a TCP app for the first time, instead of showing the VNet panel and starting VNet like we do now, we should instead open the marketing tab. Subsequent clicks on "Connect" after the user has started VNet at least once should skip opening the marketing tab and instead open the VNet panel and start VNet straight away.

This behavior should make it so that people who have been using VNet before the marketing tab was added will not see it (as they already know what VNet is). Since we're likely to store the information about whether the user launched VNet or not in app_state.json, it should also handle a situation where the user data folder is removed and the user starts VNet through the panel. In that case, the tab won't be shown.

The tab should be accessible through the question mark icon in the VNet tab which currently opens the docs. However, if the user is not logged in to any cluster, it's not possible to open a new tab. In that case, the icon should open the docs like it does now.

• Create the marketing tab.
• Integrate it with the first VNet launch.
• Integrate it with VNet deep link in Web UI.