Don't suggest insiders program nor show start page when in codespaces

[luabud]

Right now we show two separate prompts for the Jupyter and the Python extension insiders program, when we first see someone in VS Code Insiders. I'm wondering if we could display just one notification prompt to include users in both programs at once. Users would still be able to opt in to each program separately from extensions, this would be just to avoid over prompting notifications.

---

Update: changing this to drop the notifications when in a codespace, as well as the start page.

[luabud]

FYI @claudiaregio @greazer

[aeschli]

Codespaces currently use Insider builds, and have the regular Python extension installed by default. Because of that, all Codespaces users see the notifications the first time a Python file is opened. That's confusing for new users.

I suggest to only recommend the insiders program to power users. Don't show the dialog on the first activation of the Python extension. Better wait for more advanced commands, or only recommend when a user has used the Python extension for a week or more.