Add legacy rps

[mkflow27]

This pr adds the following additions:

• Adds legacy rateProviders and introduces LegacyReview.md
• Adds ChainLinkRateProviders and introduces ChainLinkRateProvider.md
• Adds "fantom" as a network entry & adds sftmx
• Adds linter
• Adds json Schema validation
• Adds github actions which validate the registry.json

Before this gets merged we should aim to add all the remaining assets to the RateProviders. Outstanding

• Update not added assets.

After this pr has been merged

• Handle Grandfathering of rate providers from pre-repo days #46
• review: add generic reviews #56
  will be closed.

[mkflow27]

Factory needs updating

[franzns]

Thank you @mkflow27 for these changes. I like the schema validation you put in place!

[Zen-Maxi]

Looks good to me with the revised review md files and formatting. Maxis will take responsbility of adding Chainlink rate providers as they are created as well as any others if they are not already included in this list.