✨Implement amp-ad-exit indirect targets

[jyn15]

Implement option 2 of #26241

/cc @clawr

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[lannka]

could you also add an e2e test for this?

/test-e2e/test-amp-ad-exit.js

[jyn15]

Added e2e tests. I tried to run e2e tests locally
gulp e2e --files=extensions/amp-ad-exit/0.1/test-e2e/test-amp-ad-exit.js --nobuild
it seems the tests are already failing on master branch for these environments:
AmpdocEnvironment.A4A_INABOX_FRIENDLY, AmpdocEnvironment.A4A_INABOX_SAFEFRAME

[lannka]

@powerivq to help with the e2e tests

[jyn15]

Updated implementation to reflect the changes in the proposal #26241 (comment)

[jyn15]

Friendly ping :)