feat: init command support for starknet

[xJonathanLEI]

As part of the effort of adding Starknet to The Graph Network, this PR adds a new protocol Starknet to the init command with 2 networks: starknet-mainnet and starknet-sepolia. It's built on the substreams-starknet crate.

Similar to Ethereum, this implementation bootstraps a full substreams project with 3 sinks: sql, clickhouse, and subgraph, all of which have been tested against firehose-starknet v0.2.2.

A notable difference from Ethereum is that, while the Starknet Firehose protocol does indeed provide access to contract events (which is how Starknet support in graph-node works after all), there is currently no complete ABI-based event decoding implementation in Rust for Starknet, making it difficult to generate an actually useful Starknet substreams project automatically.

Therefore, the template implemented in this PR simply tracks block metadata instead. These fields are indexed:

• hash
• prev_hash
• height
• timestamp
• tx_count
• event_count

Once we have the ABI decoding implementation ready, I will send another PR to change the template to track contracts instead.