feat(routing): external redirects

[ematipico]

Changes

Closes PLT-2745

This PR adds support for external directs in the redirects configuration:

• Added a new error in case the user specify a URL that doesn't start with http:// or https:// or the URL isn't parsable
• No special handling for patterns. Astro can't know if the external an Astro site, so it's virtually impossible to handle route patterns e.g. [...slug], [slug]
• No particular handling inside underscore-redirects (apart from tiny refactors)

Testing

Added new tests

Docs

withastro/docs#10704

/cc @withastro/maintainers-docs for feedback!

[changeset-bot]

🦋 Changeset detected

Latest commit: 7038546

The changes in this PR will be included in the next version bump.

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[codspeed-hq]

CodSpeed Performance Report

Merging #12979 will not alter performance

_{Comparing feat/external-redirercts (7038546) with main (1a026af)}

Summary

✅ 6 untouched benchmarks

[github-actions]

This PR is blocked because it contains a minor changeset. A reviewer will merge this at the next release if approved.

[florian-lefebvre]

LGTM! This requires no changes at the adapter level right?

[ematipico]

LGTM! This requires no changes at the adapter level right?

It shouldn't

[sarah11918]

Looks great @ematipico ! Just a suggestion of what you could do in case you wanted to add a little hype to the changeset. Choose whatever kind of wording you want, but I think 2 sentences works nice here: one to link to redirects for reference, and one to explicitly say "provide a URL" to introduce the code sample.

[florian-lefebvre]

@ematipico the build is failing, I think that's because of this deletion 6a03c29 (#12979)

[sarah11918]

Ah, probably the end syntax here?