Optimize network configuration architecture, support external chain submit RPC endpoint and subquery GraphQL endpoint configuration by PR

[yakio]

• Open source SubQuery schema/template so that external chain can deploy and host the node by themselves.
• Submit PR to include the RPC endpoint and subquery GraphQL endpoint into the menu.
• Automatically check the format and usability of PR (subsequent manual review will be carried out)
• Update README to provide instructions.

[yakio]

• Logo
• Network
• RPC endpoint
• Subquery endpoint
• explorer (optional)
• Theme Color #xxxxxx
  ? Token/SS58(metadata)