Rename Integration API property 'entrypoint' to support change in Astro v4

[rodynenko]

Astro v4 rename injectRoute's argument property entryPoint to entrypoint. https://docs.astro.build/en/guides/upgrade-to/v4/#renamed-entrypoint-integrations-api

To support both v3 and v4 we can pass both entryPoint and entrypoint.

[jlarmstrongiv]

Thanks @rodynenko ! I ended up dropping support for Astro v3 since it creates errors. I credited you on the release commit though 👍