Add contracts supply endpoint

[abchrisxyz]

API:

• contracts/supply?token_id=<token_id>

Returns total ERG or token supply in contract addresses.

For ERG, this could be interpreted as TVL, although not all contracts are DeFi related.
Tokens base supply is often held in a contract (SigUSD bank contract for instance), so results are less straight forward to interpret. In some cases, addresses/{address}/balance can be used to deduce the base supply (again, SigSUD is a good example here).

[abchrisxyz]

Add option to exclude treasury contract:

contracts/supply?token_id=<token_id>&include_treasury=false

Document it likely is only relevant for ERG

[abchrisxyz]

Consider accepting a list of addresses to exclude.

[abchrisxyz]

Keep it simple and exclude coinbase and treasury addresses at all times.

[abchrisxyz]

Done in 79e5bfd