feat: add more feeder sources

[alchemist-ti]

Reolves:https://github.com/classic-terra/core/issues/230, re-support currencylayer and fixer for more fiat rate providers

[nghuyenthevinh2000]

Oh, I saw your comment, those two needs 99$ plan?

• https://currencylayer.com/product (60$/month)
• https://fixer.io/product (99$/month)

@alchemist-ti @LuncBurner

I did an estimation, each oracle makes like around 250000 req/month

Maybe, we will want to sample validator opinions first since that is a lot of added cost

[alchemist-ti]

Oh, I saw your comment, those two needs 99$ plan?

• https://currencylayer.com/product (60$/month)
• https://fixer.io/product (99$/month)

@alchemist-ti @LuncBurner

I did an estimation, each oracle makes like around 250000 req/month

Yes, If it's 250000 req/month, currencylayer.com needs 60$/month.

Here are some other options that cost less: https://github.com/classic-terra/core/issues/230#issuecomment-1581656507 seems spend less.

[inon-man]

LGTM