[APMSVLS-433] Disable DD_TRACE_STATS_COMPUTATION_ENABLED by default (#1186)

## Overview

We have confirmed that Java now has enabled client-side stats by
default. This should be disabled.

The datadog_wrapper file is where we should add this configuration env
var. [datadog-lambda-extension/scripts/datadog_wrapper at
1454b86 ·
DataDog/datadog-lambda-extension](https://github.com/DataDog/datadog-lambda-extension/blob/1454b861409ff49478c25cc5ece68efb46374add/scripts/datadog_wrapper)
It is the script that is run prior to the execution of a lambda
function. We will want to set DD_TRACE_STATS_COMPUTATION_ENABLED=false.

We should do this globally in that file, as opposed to just for Java,
since eventually we will need it from dotnet as well.

## Testing

### 1. Java lambda function e2e testing app
- **CASE 1:** `DD_TRACE_STATS_COMPUTATION_ENABLED` not configured in AWS
UI
  - `tracerMetricsEnabled=false` in tracer debug logs
- **CASE 2:** `DD_TRACE_STATS_COMPUTATION_ENABLED=true` configured in
AWS UI
  - `tracerMetricsEnabled=true` in tracer debug logs

### 2. .NET lambda function e2e testing app
- **CASE 1:** `DD_TRACE_STATS_COMPUTATION_ENABLED` not configured in AWS
UI
  - `"stats_computation_enabled": false` in tracer debug logs
- **CASE 2:** `DD_TRACE_STATS_COMPUTATION_ENABLED=true` configured in
AWS UI
  - `"stats_computation_enabled": true` in tracer debug logs

Author: eunskin

scripts/datadog_wrapper

@@ -44,6 +44,11 @@ fi
 
 debug_log "The runtime is $AWS_EXECUTION_ENV"
 
+# Disable DD_TRACE_STATS_COMPUTATION_ENABLED by default for all runtimes
+export DD_TRACE_STATS_COMPUTATION_ENABLED="${DD_TRACE_STATS_COMPUTATION_ENABLED:-false}"
+
+debug_log "DD_TRACE_STATS_COMPUTATION_ENABLED: $DD_TRACE_STATS_COMPUTATION_ENABLED"
+
 # if it is .NET
 if [[ "$AWS_EXECUTION_ENV" == *"dotnet"* ]]
 then