Support eTracker Content blocking ("data-cb-src" replacing "src" in iframes)

Problem/Motivation

eTracker now has a new Consent Manager feature, which also supports content blocking.
To allow content blocking, it needs to replace the iframe src with iframe data-cb-src.

eTracker has no auto blocking and doesn't plan such, so this would be the "only" option.

Technically, we could copy the logics like filters and libraries hooks from COOKiES module → .

(Until we need this ourselves, we won't implement this, but you can hire us for paid implementation)

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes