feat: add support for multi chain indexing

[Sekhmet]

Summary

Few forced changes for consumers:

• ORM now requires indexer to be specified to know which indexer entity belongs to.
• Things had to move around CheckpointConfig, CheckpointsOptions and OverridesConfig (new, used for database options, like decimals as it needs static config for ORM).

const mainnetConfig = createConfig('mainnet');
const sepoliaConfig = createConfig('sepolia');

const mainnetIndexer = new starknet.StarknetIndexer(createStarknetWriters('mainnet'));
const sepoliaIndexer = new starknet.StarknetIndexer(createStarknetWriters('sepolia'));

const checkpoint = new Checkpoint(schema, {
  logLevel: LogLevel.Info,
  prettifyLogs: true
});

checkpoint.addIndexer('mainnet', mainnetConfig, mainnetIndexer);
checkpoint.addIndexer('sepolia', sepoliaConfig, sepoliaIndexer);

Test plan

• Test against updated checkpoint-template
• Test against updated sx-api