Set the log level to LOG_LEVEL env variable

[sebsto]

Set the log level to LOG_LEVEL env variable

Motivation:

LOG_LEVEL environment variable was not used

Modifications:

I made the following changes to LambdaRuntime

• transform log from let to var (I hope it does not impact Swift 6 language mode)
• Set the logger logLevel to the value of the ENV varaibale, defaulting to .info when the value is incorrect or not set

By setting the log level at the creation of the runtime, before entering in the loop, I know that a change of the value in the Lambda console will not affect running microVM. Only microVM launched after the change will pick up the new value, which will eventually affect all containers as the Lambda service replaces microVM on a regular basis.

The alternative is to set the log level before each invocation of the user-provided handler. This approach would be less performant as it would require to read the environment variable at each invocation of the runtime, not only at the start.

This is a tradeoff for performance instead of flexibility.

Result:

It is now possible to write context.logger.debug("..") and read the line in CloudWatch logs