amphtml: Support npa ads and rtc blocking for on accepted consent

Describe the new feature or change to an existing feature you’d like to see

On an AMP page that uses <amp-ad> and <amp-consent> component to manage GDPR consent, we would like to have the ability to block rtc calls and serve npa ads when an EU user accepts to opt-in into data tracking.

Currently the way <amp-ad> and <amp-consent> are working is:

GDPR
- Accept: full ads + rtc calls on
- Unknown: npa + rtc calls off
- Reject: npa + rtc calls off

The way we would like it to work is:

GDPR
- Accept: npa ads + rtc calls off (when explicitly giving some extra config flag to serve npa ads with rtc calls off)
- Unknown: npa + rtc calls off
- Reject: npa + rtc calls off

The reason we want to do that it’s because for GDPR the solution that best fit us as per our legal team recommendations was that when an EU user’s preference is accepted we should serve npa ads and the header bidders should be off. We enable our header bidders through rtc calls so that’s why we want to have the ability to shut down rtc calls on an accepted consent preference.

So far the way we serve npa ads is through the data-npa-on-unknown-consent="true" flag on <amp-ad> meaning that when the EU user has unknown or rejected consent it would serve npa ads. We also have the data-block-on-consent flag set to default on <amp-ad>.

The solution we propose is to have some additional config flags on <amp-ad> that allow us to set npa ads and turn off rtc calls explicitly when the user give the accept preference to <amp-consent> .

Describe alternatives you’ve considered

One of the alternatives we considered was set the data-block-on-consent flag for <amp-ad> to _auto_reject so no matter what preference the user had, we were expecting that for the <amp-ad> component it would be auto-rejected and npa ads and rtc calls would be off. But when testing that approach it didn’t work that way, when we expressed the accepted preference it served full ads + rtc calls on.

Additional context

None.