Remix Plugin: Make constructor arguments optional

[kuzdogan]

When watching the video below I noticed the constructor arguments popped up and later in the video it causes some confusion.

I think we should make this clear that this is not required. AFAIK this is only needed for Etherscan. And even for Etherscan this might not be required. Let's check if it's indeed possible to verify without these on Etherscan. If so make it really clear that this field is optional. If it's required for Etherscan, let's only show this when Etherscan is enabled and let the user know this is needed for Etherscan. We know Sourcify does not require this (although we appreciate if provided), we should also check Blockscout and Routescan for that.