[feature]: notification e-mails rely on external components in a self hosted environment

Is there an existing issue for this?

• I have searched the existing issues

Summary

We are evaluating Plane self-hosted for our company, and thunderbird - which blocks external links by default for privacy and security reasons - blocked several resources, mainly images and logos.

In a self-hosted environment, where privacy concerns may be present and firewall rules also block some things, it seems to be that it would be good that everything in the e-mail comes from the self-hosted plane rather than any external resources.

• Images coming from https://plane-marketing.s3.ap-south-1.amazonaws.com/plane-assets/emails/
• Social icons in the footer coming from https://creative-assets.mailinblue.com/editor/social-icons/

Why should this be worked on?

For many reasons, such external resources may be blocked in the e-mail client or company network.