Add option to add Ecomail tracking code

Problem/Motivation

Ecomail offers a tracking code, allowing website owners to track contact events (see https://support.ecomail.app/en/articles/5242260-tracking-code-implementa...). While some users will probably add this code using external JS snippet system like GTM, we should still offer possibility to inject this snippet directly.

Additionally, we should offer a possibility to track user based on account e-mail abd offer a hook allowing to profide it by some other means (https://support.ecomail.app/en/articles/6563847-how-to-manually-track-us...).

This can probably happen after version 1.0 is released.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes