Extend the AWS session expiry time for the replication script
Extend the AWS session expiry time for the replication script

- This brings this aws assume-role command in line with the one in
  `govukcli` - 7bea99bd54e77b2b1f48673dbbb9b75bc45f299e - and
  extends the duration from one hour to the maximum of eight hours.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet