Move GTM id from env to wagtail settings, and add experimental secondary GTM id

[helenb]

Description of Changes Made

Request via slack to add a secondary GTM container. Advice seems to be mixed about whether this is a good idea, and whether the dataLayer should be renamed if a second container is used. Putting this on staging so that Olly can experiment.

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[engineervix]

Thanks @helenb I've reviewed the changes and they look good to me.

Just a thought (non-blocking) on the template, I wonder whether it'd make sense to create a template include for the GTM markup, so that it's defined in one place and we don't repeat ourselves. Then we'd just pass the tag manager ID when including it.

[helenb]

Thanks @helenb I've reviewed the changes and they look good to me.

Just a thought (non-blocking) on the template, I wonder whether it'd make sense to create a template include for the GTM markup, so that it's defined in one place and we don't repeat ourselves. Then we'd just pass the tag manager ID when including it.

Good idea!

[helenb]

Thanks @helenb I've reviewed the changes and they look good to me.
Just a thought (non-blocking) on the template, I wonder whether it'd make sense to create a template include for the GTM markup, so that it's defined in one place and we don't repeat ourselves. Then we'd just pass the tag manager ID when including it.

Good idea!

I might leave for now, till we know whether we want to rename the dataLayer or not for the second tag.