Add 3x Upscale option on the Web UI (invoke-ai#442)

Author: glonlas

static/dream_web/index.html

@@ -98,6 +98,7 @@ <h1>Stable Diffusion Dream Server</h1>
           <select id="upscale_level" name="upscale_level" value="">
             <option value="" selected>None</option>
             <option value="2">2x</option>
+            <option value="3">3x</option>
             <option value="4">4x</option>
           </select>
           <label title="Strength of the esrgan (upscaling) algorithm." for="upscale_strength">Upscale Strength:</label>