Allow environment extension before parsing cli arguments

[theethernaut]

I'm working in an interactivity plugin, that uses enquirer to collect arguments that were not provided when calling any task.

For example, if one were to call npx hardhat run (notice the <script> argument missing), this would produce the error:

Error HH307: Missing positional argument script

With this plugin, you would instead get:

? Enter script (A js file to be run within hardhat's environment): › ...

This is easily done by traversing all the tasks in the hre and changing isOptional to false, given that in my interactive mode, all arguments are treated equal.

However, the plugin throws when I reach this point, because environment extensions occur right after argument parsing.

I believe that giving us the option to modify task definitions before parsing occurs should be as simple as moving the line that creates the Environment object in packages/hardhat-core/src/internal/cli/cli.ts a few lines up.