improve(refiller): Overhaul refiller config

[pxrl]

The existing array-based config requires a lot of repetitive config for each chain. This scales poorly as additional chains and accounts are added.

[pxrl]

Example of the intended config:

{                                                                                                                                                                                                                                                              
  "0xc186fA914353c44b2E33eBE05f21846F1048bEda": {                                                                                                                                                                                                              
    "1": { "target": 10, "trigger": 2, "isHubPool": true },                                                                                                                                                                                                    
  },                                                                                                                                                                                                                                                           
  "0x07aE8551Be970cB1cCa11Dd7a11F47Ae82e70E67": {                                                                                                                                                                                                              
    "56": { "target": 0.5, "trigger": 0.2 },                                                                                                                                                                                                                   
    "137": { "target": 500, "trigger": 50 },                                                                                                                                                                                                                   
    "143": { "target": 200, "trigger": 100 },                                                                                                                                                                                                                  
    "999": { "target": 3, "trigger": 1 },                                                                                                                                                                                                                      
    "9745": { "target": 300, "trigger": 100 },                                                                                                                                                                                                                 
  },                                                                                                                                                                                                                                                           
  "0xf7bAc63fc7CEaCf0589F25454Ecf5C2ce904997c": {                                                                                                                                                                                                              
    "1": { "target": 20, "trigger": 6 },                                                                                                                                                                                                                       
    "10": { "target": 0.2, "trigger": 0.1 },                                                                                                                                                                                                                   
    "56": { "target": 0.2, "trigger": 0.1 },                                                                                                                                                                                                                   
    "130": { "target": 0.2, "trigger": 0.1 },                                                                                                                                                                                                                  
    "137": { "target": 0.2, "trigger": 0.1 },                                                                                                                                                                                                                  
    ...                                                                                                                                                                                                                                                        
  }                                                                                                                                                                                                                                                            
}

[pxrl]

nb. naming is temporary - if we migrate to this format I'd anticipate deprecating REFILL_BALANCES and stealing its name.