Runtime environment variable support for log level

[uncaught]

Follow up to #357

It is inconvenient to have environment variables only be applied at container build time. This kind of defeats the purpose of environment variables and makes pre-building the container impossible.

By simply removing levelToMonologConst and using the parameters as they are, everything works beautifully at runtime.

The only thing that won't happen is the thrown \InvalidArgumentException if the level is invalid. But validation of environment variables is never done at compile time in any other situation. And this validation was only introduced by #357, which, in my opinion, should not have been accepted.

To avoid a BC-break due to the validation, I'd like to see an option to disable levelToMonologConst. I've checked all monolog handlers that use the level coming from levelToMonologConst and all of them use Monolog\Logger::toMonologLevel to cast the level. There is no need to cast the level in this extension at build time. You might then make that the default behavior in a new major version and drop it eventually.

Would you be open to this change? What arguments are there for still having levelToMonologConst?

Is that validation even a BC-break if it was simply removed? It's not like a missing config validation will make anything stop working.

[GromNaN]

I have the same issue and made a PR that converts the value at runtime #446. I think there is no need for a breaking change nor a new option.