flag --apiKey no longer working with version 12

## Bug Report

**Current Behavior**

I did an upgrade of the plugin from version 6 to version 12. With version 6, the following command would run without any issues.

`serverless offline start -s local --host=0.0.0.0 --apiKey local`

Now, with version 12, the plugin says that `--apiKey` is not a valid option, even though is still present in the latest documentation.

(https://www.serverless.com/plugins/serverless-offline)

Any idea why? If this option has been removed, could you please update the documentation accordingly and provide an alternative way to set up an apiKey?

Thanks,

Bernat

Start by reproducing the command `serverless offline start -s local --host=0.0.0.0 --apiKey local` with plugin versions 6 and 12, then inspect the plugin's command-line option handling and the linked serverless-offline documentation. Done means either `--apiKey` works again or the documentation clearly removes it and explains the supported alternative.

Written by the indexing model from the issue text.