Add missing migrations for ea_sea_levels

I'm not sure why these migrations were required. Test thoroughly after
deploying this one.

```
ALTER TABLE "ea_sea_levels_measurement" ALTER COLUMN "datetime" DROP
DEFAULT;
ALTER TABLE "ea_sea_levels_measurement" ALTER COLUMN "measurement" DROP
DEFAULT;
ALTER TABLE "ea_sea_levels_station" ALTER COLUMN "chart_datum_offset"
DROP DEFAULT;
ALTER TABLE "ea_sea_levels_station" DROP CONSTRAINT
ea_sea_le_location_id_1f9d264fb849759f_fk_locations_location_id;
ALTER TABLE "ea_sea_levels_station" ADD CONSTRAINT
ea_sea_le_location_id_70a2fb63b8676ead_fk_locations_location_id FOREIGN
KEY ("location_id") REFERENCES "locations_location" ("id") DEFERRABLE
INITIALLY DEFERRED;
ALTER TABLE "ea_sea_levels_station" ALTER COLUMN "location_id" DROP
DEFAULT;
ALTER TABLE "ea_sea_levels_station" ALTER COLUMN "site_datum" DROP
DEFAULT;
ALTER TABLE "ea_sea_levels_station" ALTER COLUMN "station_id" DROP
DEFAULT;
ALTER TABLE "ea_sea_levels_station" ALTER COLUMN "station_name" DROP
DEFAULT;
```

[#77272214]
Merge pull request #76 from sealevelresearch/add-missing-migrations-ea-sea-levels

Add missing migrations for ea_sea_levels