maybe rename dynamic configuration to runtime app configuration

[michelleN]

We use dynamic config and runtime config interchangeably. It'd be nice to just use one term.
https://spinframework.dev/v3/dynamic-configuration

[itowlson]

I believe we've used dynamic config for configuration through variables, and runtime config for configuration via the runtime config file. So we shouldn't merge the usages directly, but we should review what terms we use and how we use them, and clarify in particular the variables one.

[itowlson]

Ah, looking at the page, that does now seem to be only about the runtime config file. Updating!