* satellite/satellitedb: Alter nodes disqualification column
Change the type of the 'disqualification' column of the nodes table from
boolean to timestamp.
* overlay/cache: Change Disqualified field type
Change the Disqualified field type the NodeDossier struct type from bool
to time.Time to match with the disqualified type used by the DB layer.
* satellite/satellitedb: Update queries uses disqualified
Update the queries which uses the disqualified column due to the column
type has been changed from boolean to nullable timestamp.
* docs/design: Update disqualification due impl changes
Update the disqualification design document to contain the architectural
change required to be able to restore unfair disqualified nodes in case
of an unexpected cause (bug, mistake, hard network disconnection, etc.).
