chore: use handle-mongo-error utility to generate error string for Database error

[tshuli]

Extension of #602

[liangyuanruo]

Application code is using new DatabaseError(getMongoErrorMessage(error))

[karrui]

Not all, we should also return database errors with handle-mongo-error.ts#transformMongoError instead of getMongoErrorMessage too, for better error typings instead of just the message. Most of our code is still returning with

return new DatabaseError('some message')

instead of

return transformMongoError(error)

which can give more specific errors.

Probably not a priority though, as we usually do not discriminate between the various database errors.