feat: document new entrypoints

[ematipico]

Description (required)

This PR documents a new upcoming feature for Astro v5, where the entrypoints of some functions can now accept URL other than a string

For Astro version: 5.0.0. See astro PR #12226.

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[ArmandPhilippot]

@sarah11918 I think there is only one example where Added in: was in the middle of the section. I finally found it, it was next(). Chris and I found this a little strange, so what we decided was:

• Write the type including the changes under the title
• Do not add Since
• Write in full "Since Astro v...," at the beginning of the sentence introducing the new type/parameter.

So I guess we could do the same thing here to be consistent? On the other hand these are two pages that have not yet been updated with the API format.

[sarah11918]

Thanks for looking into this @ArmandPhilippot , and yes, I noticed that these don't seem to be updated in general for our new API reference. So, I would say especially for beta docs, we can merge as-is, and then look at updating these two pages eventually to match our format. Merging then changing is less chaotic when these pages aren't being immediately translated underneath us. 😄

@ematipico , I'm just making all the wording consistent, then this one is fine to merge for the beta release!