Provide handy API fetch_contracts to access on-chain contracts - Subtask #32

[MaciejBaj]

Description

Implement the search for contracts.

As part of the previous work ok #32 there has already been implemented inserting and getting contracts registry entries in the storage already. This task is about fetching them in a handy way using with query parameters.

Additionally, add smart contract metadata and make it browsable.

• Bonus - consider Runtime API implementing text search on code_txt

Acceptance Criteria

• Implement runtime API for on-chain contracts.
• Adds metadata to contracts entry (based on ETH)
• Implement fetch_contracts API entry and provide useful handlers to query data
  • by the author (has an address) → like an address
  • by id
  • by contract info - refcount (vvm tracked) - how many different contracts use it
  • by additional metadata ( tags + name + ... + standards )
• Cover with unit tests using Runtime RPC
• Bonus - fuzzy search by text on code - consider bringing back the regex library since Runtime API can use std lib