Document what OpenTelemetry defaults make sense to change for use with Sentry

[adinauer]

Description

Document what OpenTelemetry defaults make sense to change for use with Sentry, e.g.:

• MongoDB queries do not have values but just ? placeholders in the statement, there is a flag to change this in OpenTelemetry (https://opentelemetry.io/docs/zero-code/java/agent/instrumentation/#db-statement-sanitization) we don't want to be recording query values
• HTTP headers are missing

Also add a note to warn about potential PII.

[adinauer]

Already documented in https://docs.sentry.io/platforms/java/tracing/instrumentation/opentelemetry/#capturing-http-headers but we'll need to update them to also mention sendDefaultPii and potential PII risks. After #4102 has been released, we no longer send the headers in span/transaction data but only the request object.