Add `$SENTRY_SPOTLIGHT` env var support to all SDKs

[BYK]

Persona: you are a person who's new to a code base, trying to understand how everything works together.

Assumption: It's a challenge to find all the places Sentry SDKs are initialized let alone change them conditionally for Spotlight (spotlight: true only in dev mode).

Solution: If you can just export $SENTRY_SPOTLIGHT=1 in your shell and run all the services, all applicable Sentry SDKs automatically get set up for Spotlight and you can use the "external" UI (electron or dedicated web UI)

Most popular SDKs so far:

• JavaScript
• Python
• React Native
• Java
• Ruby
• Android
• Cocoa
• Golang
• .NET
• Dart
• PHP (Laravel)

Side quest

• Explore the usage of $SENTRY_DSN in existing SDK setups which should let us use the Spotlight DSN hack easily for SDKs not natively supporting Spotlight.