Adding alternative to NetworkRigidbody (#2123)

Uses Lerp to set position and velocity

Assets/Mirror/Components/Experimental/NetworkLerpRigidbody.cs

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+using UnityEngine;
+
+namespace Mirror.Experimental
+{
+    [AddComponentMenu("Network/Experimental/NetworkLerpRigidbody")]
+    //[HelpURL("https://mirror-networking.com/docs/Components/NetworkLerpRigidbody.html")]
+    public class NetworkLerpRigidbody : NetworkBehaviour
+    {
+        [Header("Settings")]
+        [SerializeField] internal Rigidbody target = null;
+        [Tooltip("How quickly current velocity approaches target velocity")]
+        [SerializeField] float lerpVelocityAmount = 0.5f;
+        [Tooltip("How quickly current position approaches target position")]
+        [SerializeField] float lerpPositionAmount = 0.5f;
+
+        [Tooltip("Set to true if moves come from owner client, set to false if moves always come from server")]
+        [SerializeField] bool clientAuthority = false;
+
+        float nextSyncTime;
+
+
+        [SyncVar()]
+        Vector3 targetVelocity;
+
+        [SyncVar()]
+        Vector3 targetPosition;
+
+        /// <summary>
+        /// Ignore value if is host or client with Authority
+        /// </summary>
+        /// <returns></returns>
+        bool IgnoreSync => isServer || ClientWithAuthority;
+
+        bool ClientWithAuthority => clientAuthority && hasAuthority;
+
+        void OnValidate()
+        {
+            if (target == null)
+            {
+                target = GetComponent<Rigidbody>();
+            }
+        }
+
+        void Update()
+        {
+            if (isServer)
+            {
+                SyncToClients();
+            }
+            else if (ClientWithAuthority)
+            {
+                SendToServer();
+            }
+        }
+
+        private void SyncToClients()
+        {
+            targetVelocity = target.velocity;
+            targetPosition = target.position;
+        }
+
+        private void SendToServer()
+        {
+            float now = Time.time;
+            if (now > nextSyncTime)
+            {
+                nextSyncTime = now + syncInterval;
+                CmdSendState(target.velocity, target.position);
+            }
+        }
+
+        [Command]
+        private void CmdSendState(Vector3 velocity, Vector3 position)
+        {
+            target.velocity = velocity;
+            target.position = position;
+            targetVelocity = velocity;
+            targetPosition = position;
+        }
+
+        void FixedUpdate()
+        {
+            if (IgnoreSync) { return; }
+
+            target.velocity = Vector3.Lerp(target.velocity, targetVelocity, lerpVelocityAmount);
+            target.position = Vector3.Lerp(target.position, targetPosition, lerpPositionAmount);
+            // add velocity to position as position would have moved on server at that velocity
+            targetPosition += target.velocity * Time.fixedDeltaTime;
+
+            // TODO does this also need to sync acceleration so and update velocity?
+        }
+    }
+}

Assets/Mirror/Components/Experimental/NetworkLerpRigidbody.cs.meta

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