Set linker object in gtag within the Ads tag

[nfmohit]

Feature Description

Unlike Analytics, the Ads module does not set a linker object in gtag within its tag. This should be addressed in such a way so that when both Analytics and Ads modules are connected, only one linker object is set.

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Acceptance criteria

Implementation Brief

Test Coverage

QA Brief

Changelog entry

[aaemnnosttv]

This seems to have been missed in #8518 as the linker is added to the Ads tag for AMP but not for web. I think this should probably be applied in GTag rather than specific tags since it appears to be a top-level setting. It was only included as part of the tag-level configuration for GA4 for backwards compatibility since this is where all gtag options were filterable originally. Even then, it was pulled out and added as a set rather than being included in a tag config command. Since Ads was initially implemented via Analytics this would have covered both, but now that they're independent, it can be missing if only Ads is connected.