feat: add devtools updates

[ignatiusmb]

Originally from sveltejs/svelte-devtools#213
Prerequisite for sveltejs/svelte-devtools#207

[dummdidumm]

Can you add a comment to the code explaining why we need this?

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
svelte-dev	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Oct 28, 2024 6:37pm

[ignatiusmb]

Added a comment on top of the file. I haven't really thought of other plans for /devtools, but I'd guess we'd want to compartmentalize this into its own route, instead of https://svelte.dev/updates.json.

[Rich-Harris]

What happens if we're rate-limited (or the request fails for some other reason) as we're trying to prerender?

Note also that this won't update when the tags update, only when the tags update and we've redeployed the site, which depending on what other activity is happening could be a long delay.

We could try making it an ISR route? Otherwise I think it has to live elsewhere

[ignatiusmb]

The tags not updating until we redeploy the site is a concern indeed, I thought it'd be fine for users to wait but it could theoretically take days or weeks before the site is redeployed.

Making this an ISR route seems to be the sweet spot, rate limits shouldn't be a concern as GH allows 60 reqs/h — unless I'm mistaken about how ISR works and it only caches for each unique IP requests? Which.. I haven't thought about how to tackle in that case

This update manifest needs to be hosted under https and I initially thought about spinning up its own site under https://devtools.svelte.dev or something but it seems like too much just to host a single file. Do you have any ideas if this were to 'live elsewhere'? One other alternative I can think of would probably be GH pages

[Rich-Harris]

Converted it to an ISR route, checked and it works perfectly! It will revalidate every 5 minutes, so we should stay comfortably under rate limits.