feat(pricefeeder): overrides and default to post all

[Unique-Divine]

[k-yang]

As the number of exchanges and price symbols grow, it becomes unwieldy to maintain the entire mapping in the env variable EXCHANGE_SYMBOLS_MAP. A cleaner solution would be to have a hard-coded default set in the binary itself, and have the EXCHANGE_SYMBOLS_MAP be an override input that turns on/off certain exchanges/pairs, and adds more pairs if the hard-coded config isn't up to date.