Update user-guide to cover the requirements for cross-account access to s3 buckets.

[mikereiddigital]

User Story

As a collaborator
I need to know how cross-account access to s3 buckets hosted in core accounts such as core-shared-services is undertaken, particularly for those collaborators who may not be familiar with the mechanics.
So that collaborators have all the information at hand and don't need to raise an issue on the ask channel.

The user-guide doc to be amended is https://user-guide.modernisation-platform.service.justice.gov.uk/user-guide/working-as-a-collaborator.html

Value / Purpose

Collaborators who may be unfamiliar with modernisation-platform and the requirements for cross-account access to s3 buckets using collaborator roles.

Useful Contacts

No response

Additional Information

This is already covered here in https://user-guide.modernisation-platform.service.justice.gov.uk/user-guide/platform-user-roles.html#s3-upload but adding to

Definition of Done

• Amend user-guide as above.
• Review with colleagues in team.