Use report to store marketing automation Activity's content

The content of the marketing automation is a text field, but as shown #12713 this fields have a limit so the can be indexed.

Normally the content of a marketing email is a html code, which may contain a lot of styles and text that will be never translated.

In order to avoid the limitation, it will be great to store the content of the activity so the report translation mechanism is used to just store the translations of the relevant fields and avoid translating the full text.