Network subgraph struct

[hopeyen]

• For more flexible graphQL queries, we avoid having to generate graphql source files manually and utilize graphQL Client Response type.
• Based on response, a Network struct to keep track of network minimum indexer stake requirement and optional indexer information with helper functions implemented to access fields later
• Added QueryError type
• Unit testing for helper functions

Next steps:

• Perhaps refactor graphQL client across all endpoints
• Discuss Network query efficiency (query all indexer at once and store the data, or only query when received relevant messages)