Resolve "The mechanism to watch devices during controller start currently only supports watching the same path for each device"

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

Related to #235

controller/mocks/NetworkElement.go

@@ -20,6 +20,22 @@ type NetworkElement struct {
 	mock.Mock
 }
 
+// GetGnmiSubscriptionPaths provides a mock function with given fields:
+func (_m *NetworkElement) GetGnmiSubscriptionPaths() [][]string {
+	ret := _m.Called()
+
+	var r0 [][]string
+	if rf, ok := ret.Get(0).(func() [][]string); ok {
+		r0 = rf()
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).([][]string)
+		}
+	}
+
+	return r0
+}
+
 // GetMetadata provides a mock function with given fields:
 func (_m *NetworkElement) GetMetadata() conflict.Metadata {
 	ret := _m.Called()