Add analytics and cookie consent component

[PaulioRandall]

What does this change?

Adds analytics and cookie consent script.

Why?

Got to have analytics so it can guide where and what we work on.

Does this introduce new dependencies?

Depends on an external script by Civic Cookie Consent. This is specified within the script and not part of package.json.

https://cc.cdn.civiccomputing.com/9/cookieControl-9.x.min.js

How is it tested?

In multiple live apps including:

• https://apps.london.gov.uk/wild-and-free
• https://apps.london.gov.uk/planning/ (Script and CSS copied out of component in this case)

Minor documentation amendments have been made while adding this script to the component library.

How is it documented?

In code.

Is it complete?

• [x] Have you included changeset file?
• [x] If this adds a new component, is it exported via index.js?