Add support for consumer side customization of the actual astro config

[wise-king-sullyman]

NEEDS REFINEMENT

Currently we do not have any way of customizing the astro config file (not our pf-docs config) from the consumer side.

We need to add this support to enable consumers to make changes they may need, i.e. customization to vite.

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Jira Issue: PF-3604

[coderabbitai]

⚠️ Possible Duplicate Issue(s)

• Add ability to pass in vite / astro configurations for doc core #95

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