Support setting custom navigation links in the YAML configuration

[caendesilva]

Splitting this out so that we have one issue for authors and one for navigation links

Originally posted by @caendesilva in #1719 (comment)

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From the docs:

Note that YAML settings cannot call any PHP functions, so you can't access helpers like env() for environment variables, nor declare authors or navigation links, as you cannot use facades and objects. https://hydephp.com/docs/1.x/customization

We should find a way to support authors and navigation links from here, possibly by matching input arrays to constructors. We may want to do this in v2 as the navigation system is reworked, so we don't introduce a change that will be broken soon.

[caendesilva]

See sister issue #1719