Honor the overridden Craft mailer component

[nstCactus]

Although niche, it is a valid use case to override the Craft mailer component (see https://craftcms.com/docs/3.x/config/#mailer-component). In such cases, the plugin doesn't honor the from property of the overridden mailer component and instead forces the use of the email settings from project config (set in the control panel).

This PR corrects this behavior by always using the from property of the mailer component:

• if it hasn't been overridden, its default value is the one set in the CP
• if it has been overridden, the overridden value is used