Filter on Contract Negotiation on contractOffers

# Feature Request

On the endpoint `/management/v4/contractnegotiations/request`
the query:
```json
{
"@context":[
"https://w3id.org/edc/connector/management/v2"
],
"@type":"QuerySpec",
"filterExpression":[
{
"@type": "Criterion",
"operandLeft": "contractOffers.assetId",
"operator": "=",
"operandRight": "59dbc8a3-3a1c-4952-923e-9890a58f9194"
}
]
}
```

return a 200 with an empty array, and I have contract negotiations with this UUID.

## Why Is the Feature Desired?

It allow to retrieve negotiation event if the agreement is not yet available.

## Solution Proposal

Add mapping in the [ContractNegotiationMapping](https://github.com/eclipse-edc/Connector/blob/main/extensions/control-plane/store/sql/contract-negotiation-store-sql/src/main/java/org/eclipse/edc/connector/controlplane/store/sql/contractnegotiation/store/schema/postgres/ContractNegotiationMapping.java) ?

Start with the /management/v4/contractnegotiations/request endpoint and the example filter using contractOffers.assetId. Read ContractNegotiationMapping.java in the SQL contract-negotiation store, then reproduce the request against a negotiation whose asset UUID is known. Done means the filter returns the matching contract negotiation even when its agreement is not yet available.

Written by the indexing model from the issue text.