[ERC Registry] Add RegistryGenerator service class to handle exporting ERC contracts into JSON files

[quiet-node]

Problem

According to the design document, a new RegistryGenerator service class is needed to handle exporting ERC contracts into JSON files.

Solution

Implement a RegistryGenerator service class under tools/erc-repository-indexer/src/services/registryGenerator.ts. The class should include:

• A registryGenerator() method to output ERC contracts into JSON files

The RegistryGenerator class should also be tested using the Jest testing framework.