Add organisation meta tag if current page is org

[vanitabarrett]

Trello: https://trello.com/c/cbRSHmA9/30-add-organisation-id-to-custom-dimensions-in-google-analytics

Adds the govuk:analytics:organisations meta tag if the current page is an org (has an analytics_identifier value in the content item)

Component guide for this PR:
https://govuk-publishing-compon-pr-397.herokuapp.com/component-guide

[vanitabarrett]

@sihugh I think this will fix: https://trello.com/c/cbRSHmA9/30-add-organisation-id-to-custom-dimensions-in-google-analytics . Can you take a look, I'm not sure how it's currently set up in Whitehall so there may be a better fix

[tijmenb]

Will this conflict with https://github.com/alphagov/govuk_publishing_components/blob/master/lib/govuk_publishing_components/presenters/meta_tags.rb#L48-L60?

[vanitabarrett]

@tijmenb Potentially, although from what I could see only organisations actually have a value for analytics_identifier - the rest seem to be null. I can add a check against the document_type though to make sure we only do this for organisations?

[vanitabarrett]

@tijmenb I've adjusted the logic slightly so we only set govuk:analytics:organisations to be equal to the high level content_item[:analytics_identifier] if the document is an organisation.

[tijmenb]

I wonder if you could replace the conditional by adding this line?

organisations += [content_item] if content_item[:document_type] == "organisation"