Support for GA4 Tag Manager

[heathd]

adding support for GA4 tag manager. Can activate by setting ga4_tracking_id config variable.

I have not reviewed the custom analytics tracking javascript relating to search operations, so that may not work

What’s changed

Add support for GA4 tag manager

Identifying a user need

The GDS Engineering Enablement team need this as we are using TDT for our team documentation and would like to add google analytics support

[huwd]

Let's look at this for 4.1 there's a GTM PR below too would like to consider the two at the same time

[huwd]

@heathd you still interested in this?
I think I shelved reviewing this so we could prioritise some WCAG stuff, I meant to come back earlier but this is the first time I've returned.

Can do a quick bit of testing and get this merged for you?

[davidread]

@huwd Yes please, could you review and merge this? We're currently maintaining a fork until this is done.

Google Universal Analytics is dead, which drives the need for supporting GA4, to avoid going backwards

[huwd]

I've rebased it against main,
Will check the test suite now

[huwd]

Yeah looks reasonable and additive.

[huwd]

Interestingly fails on main now too:
https://github.com/alphagov/tech-docs-gem/actions/runs/16609419271/job/46989177300

[natf-gds]

This can't pass tests until Huw's changes are in #426

426 is replaced by #427

[davidr-gds]

🎉