Update market data api

[tomjeatt]

Big discrepancies between VDOT prices in the Oracle (which uses DIA's fair price feed) and the UI (which doesn't). This has been reported by users more than once, and is something we need to fix.

Requirements (TBC):

1. Use fair price feed where possible
2. If unavailable use DIA's standard price feed
3. If unavailable use CoinGecko

The only part that needs to be implemented is 1 as the market data api already uses DIA as the primary data source.

[tomjeatt]

Resolved with #1619