Plugin installation while running scaffold command

## Expected Behavior
After running 
`
gatewayd plugin scaffold [flags]
`
The scaffolded plugin should be installed in gatewayd automatically.

## Current Behavior
After running
`
gatewayd plugin scaffold [flags]
`
the scaffolded plugin is not installed in gatewayd and the developer needs to update the `gatewayd_plugins.yaml` file manually.
