Update access token auto-expiry documentation

What does this MR do?

Updates documentation to reflect that whether you automatically have an expiry date applied to your access token differs depending on your offering and when you upgrade to 16.0 or later. This is achieved through splitting up the existing warnings into a small warning in the create token sections, and putting the bulk of the information in new token expiry sections, with a link between them.

Also moves warnings around to make sure we do not have multiple alert boxes next to each other.

Related issues

#473099 (closed)

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