Dropped Epoch expected functionality

[Cmdv]

Original message taken from our discord channel:

Hey DB-Sync team, while checking in on the current governance actions via koios, we discovered an issue with the dropped_epoch entries.

According to the documentation:
If not null, then this proposal has been dropped at the specfied epoch. A proposal is dropped when it's expired or enacted or when one of its dependencies is expired.
the value should be set to a non-null value in case a proposal expired or got enacted.

However, tests on MainNet, SanchoNet and PreView showed, that the value for dropped_epoch is never set and stays at null.

This example was taken from epoch 582:

    "proposed_epoch": 492,
    "ratified_epoch": 493,
    "enacted_epoch": 494,
    "dropped_epoch": null,
    "expired_epoch": null,
    "expiration": 553,

The proposal was enacted and did not expire. So i think there is a bug that should be corrected that according to the documentation also enacted proposals should get an entry in the dropped_epoch value. Thanks to <@667815879488045056> and <@742729268106231941> for helping to double-check.

[HeptaSean]

Maybe related: For expired proposals, e.g., https://adastat.net/governances/51f495aa23f4b3b3aa90afde4a0e67823bb7ac4ac65f5ffbb138373b863f2f7400, the dropped_epoch is expired_epoch + 1:

    "proposed_epoch": 518,
    "ratified_epoch": null,
    "enacted_epoch": null,
    "dropped_epoch": 526,
    "expired_epoch": 525,
    "expiration": 525,

As stated in #1704 (comment) (but not followed up on), I would expect them to match (or at least a documented reason why they do not match).