feat: AWS lambda programatic wrap

[joshwestbrook]

Our company uses container images for deploying our lambda functions and use herokuish Procfile entries as our entrypoints for the images.

This means it takes a ton of jiggery-pokery to get this working for our situation because:

1. We can't natively pull in a lambda layer without using the AWS S3 CLI to pull down the layer zip and copy into our base image
2. The _HANDLER environment variable actually contains our Procfile entry (which calls the lambda RIC under the hood with the handler that's expected by this wrapper)

This PR introduces an alternative way of instrumenting by programmatically wrapping an arbitrary handler method for scenarios where using lambda layers aren't an option (such as ours).

Example:

require 'opentelemetry/instrumentation/aws_lambda'

module Example
  class Handler
    extend OpenTelemetry::Instrumentation::AwsLambda::Wrap

    def self.process(event:, context:)
      pp event
    end
    instrument_handler :process
  end
end

TODO:

• Update documentation
• Regression test the lambda layer

[joshwestbrook]

Probably need to throw some trys in here so we don't blow up if the metrics SDK isn't in use