Inconsistent Username property in configuration

[lbajsarowicz]

driver/src/System/DefaultConnection.php

Lines 67 to 70 in 8da0872

	public function getUser(): string
	{
	return $this->getValue('user', true);
	}

vs

driver/src/System/DebugExternalConnection.php

Lines 81 to 84 in 8da0872

	public function getUser(): string
	{
	return $this->getValue('username', true);
	}

Michał's edit: Let's use user for both.