Simplify Sentry meta tag retrieval

[stayallive]

This simplifies echo'ing the Sentry meta for the end-user by just needing to call:

Sentry\Laravel\Integration::sentryMeta();

This makes it easier than needing (and documenting) to do:

Sentry\Laravel\Integration::sentryTracingMeta();
Sentry\Laravel\Integration::sentryBaggageMeta();

We could even drop the "seperate" methods or make them private / internal. But keeping them around for now makes this a non-bc change which saves one more step users need to take when upgrading (but might be worth still... to be discussed).

[cleptric]

Good stuff

We could leave the methods and point people to sentryMeta via docs.
This makes the upgrade less painful imo.