Add `token_supply` to metadata on SVM

[nsjames]

The SVM token API offers a token holders route, and a token metadata route, but no way to know what the total supply of the token is. Unlike EVM routes, there is no total_supply property returned when getting a token's metadata.

A user would like to be able to calculate a holder's percentage of the total supply, but must fetch the total supply from the chain.

Origin

Discord chat in graphprotocol from CodyMe555

[nsjames]

Followup from user:

Maybe the percentage held should be adjusted and returned as part of the holders endpoint too. I mean, it's an expensive endpoint so it would make sense to maximize data richness returned there. This would avoid the token metadata call entirely and improve latency..