Indexer: search for common project practices

### Use-case description
A project developer is considering several methodological choices. They search for all other projects using the same methodology to gauge what specific common practices are.

#### Current procedure (to be enhanced)
Go to policies and search for the applicable methodology (e.g., ACM0007), open the policy and copy the policy ID. Go to “documents”/“VCs” and search “Monitoring Reports” and enter the policy ID. Note the number of Monitoring Reports. Open the first one and click “Document.” Search for specific fields (e.g., "Choose option to determine the remaining lifetime of the equipment”). Note the response (e.g., “(c) Use default values”). Repeat the process for other Monitoring Reports.

### Requirements
Enable users to conviniently search for:
- all projects (via searching for a specific artifact defining projects such as 'Monitoring Reports')
- which are executed under the same policy (i.e. by Policy ID)
- and featuring specific range or exact attribute values which represent a specific methodological decision (e.g., “(c) Use default values”).

### Definition of done

- Indexer backend and UI have been enhanced to provide access to the data as specified above
- Documentation is updated accordingly
- Corresponding Indexer APIs are implemented and documented

### Acceptance criteria
Users can specify search criteria in the Indexer UI to make necessary filtering to implement this use-case