[#488] reputation: Change Writer interface

Includes:
- Delete first `ctx` argument in `Write` method.
- Move intermediate Initial trust struct and method
to `calculator` file.
- Change Alpha to 0.1.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

cmd/neofs-node/reputation/intermediate/calculator.go

@@ -1,11 +1,23 @@
 package intermediate
 
 import (
+	"github.com/nspcc-dev/neofs-node/pkg/services/reputation"
 	"github.com/nspcc-dev/neofs-node/pkg/services/reputation/eigentrust"
 	eigencalc "github.com/nspcc-dev/neofs-node/pkg/services/reputation/eigentrust/calculator"
 	eigentrustctrl "github.com/nspcc-dev/neofs-node/pkg/services/reputation/eigentrust/controller"
 )
 
+// InitialTrustSource is implementation of the
+// reputation/eigentrust/calculator's InitialTrustSource interface.
+type InitialTrustSource struct {
+	Trust reputation.TrustValue
+}
+
+// InitialTrust returns `initialTrust` as initial trust value.
+func (i InitialTrustSource) InitialTrust(reputation.PeerID) (reputation.TrustValue, error) {
+	return i.Trust, nil
+}
+
 // DaughtersTrustCalculator wraps EigenTrust calculator and implements
 // eigentrust/calculator's DaughtersTrustCalculator interface.
 type DaughtersTrustCalculator struct {