[dss] Op. Intent handler: make mentioning OIR being updated optional in key parameter

[Shastick]

The description for the key parameter states:

Proof that the USS creating or mutating this operational intent was
aware of the current state of the airspace, with the expectation
that this operational intent is therefore deconflicted from all
relevant features in the airspace. This field is not required when
declaring an operational intent Nonconforming or Contingent, or when
there are no relevant Entities in the airspace, but is otherwise
required. OVNs for constraints are required if and only if the USS
managing this operational intent is performing the constraint
processing role, which is indicated by whether the subscription
associated with this operational intent triggers notifications for
constraints.
The key does not need to contain the OVN for the
operational intent being updated.

However the current implementation will return a 409 if the OVN of the operational intent reference is not present in the key.

This contradicts the specification, and the present PR is a suggested fix.

Note that this will require this prober PR to be merged and released for the CI to pass.