Display an onboarding Window after package installation

[bruno-garcia]

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After installing the package, users (that don't come from Sentry's in-product wizard) would need to follow instructions offline.

One way to improve the experience here is to open a window in the editor walking the user through setting things up. Including getting a DSN from Sentry and getting started.

• [ ] The window shall be displayed right after clicking: Install package
• [ ] There should be a way to open this window on demand (from SentryWindow perhaps): Covers the use case where users dismisses this window but would like to continue later
• [ ] A button for: Go away now! I know what I'm doing
• [ ] Either a clarification on how to get a DSN, or ideally: Login to Sentry, browse projects, get DSN.
• [ ] Nice to have: Wizard to select features/configure: Performance monitoring sample rate.