Add option to keep the linker for exact domain matches

Description

The Don’t append linker for exact domain match PR can affect tracking in situations where more platforms use the same domain. The request is to provide a way to opt-out of this behaviour.

Ex: In the case of WordPress.com, the linker is used to transition from the AMP Landing Pages to Calypso; which are 2 platforms with the same domain. After the linker removal for exact domain match, this transition is broken.

Alternatives Considered

Having a noInternalLinking would allow us to opt-out of the changes from the PR and go back to the previous behaviour.

Additional Context

The noInternalLinking solution has been brought up in other discussions as well: https://github.com/ampproject/amphtml/pull/32100#issuecomment-772901579 https://github.com/ampproject/amphtml/issues/30176#issuecomment-765730810

[micajuine-ho]

@claudiucelfilip Took this question to Design review yesterday. The team agreed that we can support this. I will work on making the changes with a new opt in API.

[ekatysheva]

I think so. I don’t deeply undestand what is going on when linking is working (though I’ve tried to read docs many times), but e.g. this portion of configuration

 "linkers": {
   "enabled": true,
   "proxyOnly": false,
   "destinationDomains": ["*.ourdomain.com"] // we have several subdomains for staging/prod
 },

helped me to link sessions between AMP and non-AMP pages with google analytics. It was done quite some time ago and I found out just today that this behaviour is broken when tried to do so with amplitude.