changed behaviour to raise error instead of using default db when re…

[darefalola]

Thoas has the following behaviour such that when a release version is requested via the genome uuid, one of the following happens:

• If a release is found, it is returned to Thoas.
• If gRPC connection is down, a default release version is used.
• If the release is not found, a default release version is used.

The diagram below shows a clearer view of this issue

sequenceDiagram
    title GraphQL Core Generic Workflow
    actor User as User
    participant GraphQL_BE as GraphQL UI/Backend
    participant gRPC as gRPC Service
    participant Metadata_DB as Metadata Database
    participant Mongo_DB as Mongo Database
    
    User ->> GraphQL_BE: Sends Query Request
    GraphQL_BE ->> gRPC: Request Release Version using Genome UUID
    gRPC ->> Metadata_DB: Fetch Release Version
    Note over gRPC, Metadata_DB: Example version: 110.3

    alt gRPC Connection Success
        opt Release Found in Metadata DB
            Metadata_DB -->> gRPC: Release Found
            gRPC -->> GraphQL_BE: Return Release Version
            GraphQL_BE ->> Mongo_DB: Fetch data from Mongo
            Note over GraphQL_BE, Mongo_DB: e.g., 'release_110_3' Mongo DB
            Mongo_DB -->> User: Return Fetched Data
        end

        opt Release NOT Found in Metadata DB
            Metadata_DB -->> gRPC: Release NOT Found
            gRPC -->> GraphQL_BE: Notify Release Not Found
            GraphQL_BE -->> GraphQL_BE: Fallback to "default_mongo_db"
            Note over GraphQL_BE: Default Mongo DB used as fallback
            GraphQL_BE ->> Mongo_DB: Fetch data from default Mongo (e.g., 'release_110_1')
            Mongo_DB -->> User: Return Fallback Data
        end
    else gRPC Connection FAILED
        gRPC -->> GraphQL_BE: Connection Failed
        GraphQL_BE -->> GraphQL_BE: Fallback to "default_mongo_db"
        Note over GraphQL_BE: Using default Mongo DB due to gRPC failure
        GraphQL_BE ->> Mongo_DB: Fetch data from default Mongo (e.g., 'release_110_1')
        Mongo_DB -->> User: Return Fallback Data
    end

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This PR adds a fix such that if a release is not found or gRPC connection is unreachable, it returns an error to the user rather than using a default db.