have 3rd person make a side jump

I assume that you're not using the standard character controller to learn and implement everything on your own. Check out this series from Quilly where he makes a character controller from scratch, he covers a lot of things in really great detail, I'm sure you will resolve your problem there. Helped me a lot, hope it does the same for you :)

EDIT: OK so well Quilly didn't cut it for you, that's why we're here :)

It was easier than I thought, I did it with a rigidbody attached to my player, it worked really nice for me. Here you go:

 // This enum is for convenience, you can go without it if you want, I like to stay organized :)
 public enum DodgeDirection { Right, Left, Forward, Backward }

 // This vector is essential if you want to have variants dodging amounts/forces, it represents how much the player will go to the side, up and forward
 // left: -x, right: +x, up: +y, down: -y, forward: +z, backward: -z. Don't worry you'll understand in a moment
 // if you don't want to have different forces applied to your player when he dodges left/right, forward/backward, just get rid of this vector and use a float variable instead
 public Vector3 dodge = new Vector3(5, 5, 5);

 // This is the dodging method, you just give it a direction and it will handle the rest using the `dodge` vector we previously defined.
 public void Dodge(DodgeDirection dir)
 {
         switch (dir) 
         {
             case DodgeDirection.Right:
                 rigidbody.AddForce(_transform.right * dodge.x + _transform.up * dodge.y, ForceMode.Impulse);
                 break;
             case DodgeDirection.Left:
                 rigidbody.AddForce(-_transform.right * dodge.x + _transform.up * dodge.y, ForceMode.Impulse);
                 break;
             case DodgeDirection.Forward:
                 rigidbody.AddForce(_transform.forward * dodge.z + _transform.up * dodge.y, ForceMode.Impulse);
                 break;
             case DodgeDirection.Backward:
                 rigidbody.AddForce(-_transform.forward * dodge.z + _transform.up * dodge.y, ForceMode.Impulse);
                 break;
         }
 }

 // Since we're gonna be dealing with a rigidbody and forces, we might as well use FixedUpdate
 // I used 'l', 'j', 'i' and 'k' to dodge left, right, forward and backward (respectively)
 // If I were you and using WASD controls, I would dodge left by double tapping 'A', right by double tapping 'D' etc. (With a threshold I define)
 void FixedUpdate()
 {
     if (Input.GetKeyDown("l"))
             Dodge(DodgeDirection.Right, dodge);
     if (Input.GetKeyDown("j"))
             Dodge(DodgeDirection.Left, dodge);
     if (Input.GetKeyDown("i"))
             Dodge(DodgeDirection.Forward, dodge);
     if (Input.GetKeyDown("k"))
             Dodge(DodgeDirection.Backward, dodge);
 }
 

Couple of notes:

1. In my test environment, I was using a capsule collider for my player so I had to constrain all the rotations in the rigidbody component, because since I'm adding force, the capsule would get knocked out and thrown to the ground (kinda cool effect if you want fighting in your game) - So no rotation from the rigidbody, I handled rotation myself.

2. I tried all the possible types of forces, only Impulse and VelocityChange seemed to do the trick, while Force and Acceleration didn't seem to have any effect.

3. Wondering about _transform? - I always like to cache my transform component if I'm gonna be using it a lot, because when you do transform, you're actually calling GetComponent<Transform>() - which isn't nice to call so many times. (I usually cache in Start or Awake)

4. Make sure you handle the rotation of your player well, let me know if you have trouble with that - You could use Quilly's code for that, works like charm.

Let me know how it goes, hope I helped :)