kel services create

Implement `kel services create` to create a service for the activated site. This command will take a required flag `--plugin` which will inform the service creation which plugin will provide its functionality.

Start at the CLI entry point for `kel services create` and inspect how commands parse required flags and access the activated site. Done means the command accepts `--plugin` and creates a service for that site using the specified plugin; no files or tests are identified in the issue.

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