Google tag manager and OneTrust on /-/trials/duo_pro/new pages

What does this MR do and why?

Add Google tag manager and OneTrust to Duo Pro trial pages, dataLayer code for /-/trials/duo_pro/new path - https://gitlab.com/gitlab-org/gitlab/-/issues/439033#technical-requirements

MR acceptance checklist

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Before

How to set up and validate locally

bin/rails c

Feature.enable(:duo_pro_trials)

• Setup GDK to simulate SaaS.
• Add

google_tag_manager_nonce_id: '_google_tag_manager_nonce_id_'
one_trust_id: '_one_trust_id_'

to extra section of gitlab.yml.

• Restart GDK. Sign up.
• Visit /-/trials/duo_pro/new and open page source.
• Validate GTM and OneTrust code is present.

Related to #439033