Add GA4 tracking to details in attachments

[andysellick]

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What / why

Add GA4 tracking attributes to details components within attachment components on publication pages.

The tracking for the details components is mostly handled automatically, but the component can't determine the value for index_section_count (the total number of related things being tracked) so this must be passed to the component. In this case it is the number of attachments that have a details component showing, which is not necessarily the same as the total number of attachments.

Some example pages to test:

• https://www.gov.uk/government/publications/make-a-lasting-power-of-attorney
• https://www.gov.uk/government/publications/application-for-a-vehicle-registration-certificate
• https://www.gov.uk/government/publications/attendance-allowance-claim-form
• https://www.gov.uk/government/publications/self-assessment-tax-return-sa100
• https://www.gov.uk/government/publications/new-year-honours-list-2024

Also removes some unnecessary data from the tests in the same file.

Visual changes

None.

Trello card: https://trello.com/c/xhASj1rp/765-add-tracking-to-details-component