AWS Lambda integration overwrite environment variables

### Problem Statement

Please provide a way of setting SENTRY_TRACES_SAMPLE_RATE to a custom value.

I have more than 100 lambdas and is hard to modify this value manually as it's written in the documentation

Already tried to set the environment variable on lambda before enabling the integration, but it's always overwritten when enabling the integration

### Solution Brainstorm

Check if lambda has already this environment variable configured and if yes, don't overwrite it