Skip Cloudflare for internal pix calls

[NikolasHaimerl]

          When calling this URL, the requests will go from Fly to Cloudflare back to Fly, which may increase our ingress/egress bills.

A more performant option is to route the requests internally within Fly.io only, see e.g. https://fly.io/docs/networking/app-services/#fly-io-internal-dns-and-6pn-addresses

That would require us to change our PIX server to allow requests for two hostnames - the public one at https://pix.filspark.com and the Fly-private one. See https://github.com/filecoin-station/piece-indexer/blob/1b97e24b1a972401992a57d6bc7c23f9b17e17d7/api/lib/app.js#L15-L19

Considering the complexity and time pressure, I think it's best to use https://pix.filspark.com for now.

Originally posted by @bajtos in #31 (comment)

[bajtos]

Thank you for opening this issue, @NikolasHaimerl!

I changed the title to clarify that the goal is to bypass/skip Cloudflare. The code in #31 using https://pix.filspark.com already uses Cloudflare.

[bajtos]

We have a fixed rate for the Cloudflare plan for filspark.com and AFAICT, the usage stayed mostly the same after we started to query pix.filspark.com.

We can keep using pix.filspark.com for now.