Add example of indexing Script log

[ra0x3]

• This was asked for by two different grantee teams during the leads offsite
• A script Log is just an abi::Log type
• We are familiar with these already
• However for a script Log some additional functionality is needed because the user needs to know from where the Log was created
• It was suggested that we include attribution via a Witness
  • The Witness would be include in a Transaction (e.g., via the SDK) that calls a script
• Meanwhile, on the indexer side, we would add a way for users to filter Transactions on this Witness param
  • This type of filtering logic would be included in an indexer manifest (similar to how we do with contract_id)

Additional context

• This will require a prerequisite of Add predicate support #886

[ra0x3]

Gonna close this for now, we can revisit later