Docs: Improve documentation for external / load balancer SSL termination

What does this MR do?

Customers and internal technical specialists are having difficulty navigating this document because it only uses the terminology "Proxied SSL" and does not include other common terms for the same thing.

Update the documentation to add cloud oriented terminology "External SSL termination" and "Load balancer SSL termination" (at the heading level).

Also updated the description to give troubleshooting clues - that without the disable configuration, the instance automatically attempts to configured local SSL termination and that once these configs are flipped, it stops doing that.

Added a note under Enabling HTTPS to point to the renamed section since this type of SSL termination is very common.

Related issues

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