Create an SDK checklist for Spotlight readiness

[BYK]

We need a checklist to make sure each SDK is in great shape for Spotlight integration. Will keep updating this list below:

• Ensure the SDK can be initialized without a DSN when spotlight is turned on
• Support spotlight config variable with custom URL
• Support SENTRY_SPOTLIGHT env variable for enabling Spotlight with the same semantics of spotlight config variable (bool + string)
• Ensure there's a log message indicating Spotlight is active at a specific URL
• Ensure all possible integrations are force-enabled for Spotlight events
• Ensure "source context" is working properly
• Ensure all available request data is sent to Spotlight
• If profiling is available, ensure it is turned on (future need, not needed right now)
• Ensure PII scrubbing does not apply to events sent to Spotlight