Default RPC & Indexer configuration for Lumos

[homura]

We received feedback that Lumos requires duplicate configuration for each project, such as the RPC and indexer URLs. We should consider setting these URLs as default configurations.

Describe the solution you'd like

// I am not sure if the name Provider is suitable
// Because the name Provider may cause confusion with the Provider in the Ethereum ecosystem.
interface MaybeAProvider {
  readonly indexer: Indexer;
  readonly rpc: RPC;
  readonly scripts: ScriptConfigs;

  scriptToAddress(): Address;
  addressToScript(): Script;
}

declare function createMainnetProvider(): MaybeAProvider;
decaulre function createTestnetProvider(): MaybeAProvider;