Update [runners.machine] section in Autoscaling GitLab Runner on AWS EC2 documentation

What does this MR do?

Placing MachineName (and the other options) above the first [[runners.machine.autoscaling]] solves the next runner issue

WARNING: Failed to process runner builds=0 error=failed to update executor: missing Machine options executor=docker+machine runner=r24wFd-K

Related issues

#25874 (closed)

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When applicable:

• Update the permissions table.
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