custom .plist file not added to ios project

Rename you file plist file to have a txt extension.

.plist usually need to be merged with the Info.plist of the iOS project and the .plist files are not uploaded. (Not sure what you need them for except adding info to Info.plist?)

You however can add the information you need via post process steps using the XCode Manipulation API which can be found here: https://bitbucket.org/Unity-Technologies/xcodeapi

Have a look in the forums for examples and how to use if if you are stuck. There is a lot of information available there about it, especially in the iOS and Unity Cloud Build forums.

As an example here's the code I use to set NSCameraUsageDescription. This file must be in an assets Editor/ folder

 using UnityEngine;
 using System.Collections;
 using UnityEditor.Callbacks;
 using UnityEditor;
 using UnityEditor.iOS.Xcode;
 using System;
 using System.IO;
 using System.Linq;
 using Mk.Common;
 using System.Collections.Generic;
 
 public class GveBuild {
 
     private const string NSCameraUsageDescription = "NSCameraUsageDescription";
 
     [PostProcessBuildAttribute(1)]
     public static void OnPostprocessBuild(BuildTarget target, string pathToBuiltProject) {
         Debug.Log("GveBuild.OnPostprocessBuild " + target + " " + pathToBuiltProject);
         switch (target) {
             case BuildTarget.iOS:
                 string plistFilePath = pathToBuiltProject + Path.DirectorySeparatorChar + "Info.plist";
                 // 10/5/16 The code that uses Xcode is flagged as missing in editor, but it compiles when we return to Unity and works
                 // when build is run.
                 // Q: why doesn't this work? A: 2nd link says it is fixed in 5.4.2, we'll see
                 // https://issuetracker.unity3d.com/issues/ios-monodevelop-unityeditor-dot-ios-dot-xcode-namespace-isnt-recognised-in-monodevelop
                 // https://issuetracker.unity3d.com/issues/unity-does-not-include-unityeditor-dot-ios-dot-xcode-in-project-file
                 
                 // Read the existing plist file
                 try {
                     PlistDocument plist = new PlistDocument();
                     plist.ReadFromFile(plistFilePath);
                     Debug.Log("GveBuild.OnPostprocessBuild successfully read " + plistFilePath + ": " + ValueToString(plist.root));
 
                     // Add our modifications
                     if (plist.root.values.ContainsKey(NSCameraUsageDescription)) {
                         Debug.LogError("GveBuild.OnPostprocessBuild key already set? Do not overwrite: " + NSCameraUsageDescription + " = " + ValueToString(plist.root.values[NSCameraUsageDescription]));
                     } else {
                         plist.root.values[NSCameraUsageDescription] = new PlistElementString("Camera is not used by our application (API reference is due to Unity libraries)");
                         Debug.Log("GveBuild.OnPostprocessBuild added NSCameraUsageDescription = " + ValueToString(plist.root.values[NSCameraUsageDescription]));
                     }
 
                     // Write the modified file
                     string plistPathNew = plistFilePath + ".new";
                     plist.WriteToFile(plistPathNew);
 
                     // Replace the original file. Note subsequent build steps modify the plist file further (e.g. currently facebook entries are added after this script runs)
                     if (true) {
                         // Delete the old file
                         File.Delete(plistFilePath);
                     } else {
                         // Keep the old file for diff while testing
                         string plistPathOld = plistFilePath + ".orig";
                         File.Move(plistFilePath, plistPathOld);
                     }
                     File.Move(plistPathNew, plistFilePath);
                     Debug.Log("GveBuild.OnPostprocessBuild successfully updated " + plistFilePath);
                 } catch (Exception e) {
                     Debug.LogError("GveBuild.OnPostprocessBuild PList error " + e);
                 }
                 break;
 
             default:
                 // nada
                 break;
         }
     }
 
     /// <summary>
     /// Utility to get value of a PlistElement as string
     /// </summary>
     private static string ValueToString(PlistElement element) {
         if (element is PlistElementString) {
             return ((PlistElementString)element).value;
         } else if (element is PlistElementInteger) {
             return ((PlistElementInteger)element).value.ToString();
         } else if (element is PlistElementBoolean) {
             return ((PlistElementBoolean)element).value.ToString();
         } else if (element is PlistElementDict) {
             Dictionary<string, PlistElement> values;
             return ((PlistElementDict)element).values.Select(x => x.Key + " : " + ValueToString(x.Value)).Join();
         } else {
             return element.ToString();
         }
     }
 }