Replace the 2 availability tables by a single one

[mRoca]

We currently have 2 different table for availabilties: UserAvailability and CommissionableAssetAvailability. We also have 2 repositories and every request is duplicated.

We need to replace those 2 tables by a single one. Each availability must contain a userId OR an assetId

Availability
========
id
userId (nullable)
assetId (nullable)
start
end
status
createdAt
updatedAt
history