Updated instructions for creating an API key and OAuth credentials

[MoojMidge]

First ensure that you have updated to the latest version of the addon, available here:
https://github.com/anxdpanic/plugin.video.youtube/releases/

The current latest version is
v7.3.0.1

Then follow these instructions for creating and using an API key and OAuth credentials:

Originally posted by @damnms in #1086

So for anyone else encountering this, I created a little "tutorial". This was not from scratch and i already had some things set up, so maybe a step might be missing. If so, please let me know and i add it! Be sure to follow each step. If you encounter an error, stop and fix that first! If you already have a shared key/api set up and it stopped working suddenly, maybe you did not login, see Step 12

1. Go to https://console.cloud.google.com/cloud-resource-manager?hl=de&inv=1&invt=Abnytg

2. Click on "CREATE PROJECT" in the upper line
   

3. It doesnt matter what you write in there, just click on "Create". I labeled mine "Youtube".
   

4. Easiest is now to go to https://console.cloud.google.com again, you will automatically land in the correct page for the project.
   

5. Click on "APIs & Services".

6. Click on "YouTube Data API v3" and click on "Activate"
   

7. Click on "Credentials"
   

8. Now click on "CREATE CREDENTIALS"

   8.1 Select "API Key", wait a moment and then click again "CREATE CREDENTIALS" again

   8.2 Select "Oauth-Client"

   8.3 Select "TVs and limited Input" for the "Application Type" selection. Click create and you should see it now like on the screenshot in Step 7 with one API Key and one OAuth 2.0 Client ID.

9. Now go to "Oauth Consent Screen" and add your account to the test users (recommended) OR click on "Publish" (not recommended)
   

Now you are done with YouTubes annoying setup. You have the credentials you need now. They must be used in kodi’s youtube plugin. The simplest way is to turn on the youtube configuration web function like documented in Step 10. Do NOT edit the files manually with an editor coz they will be overwritten when the youtube plugin runs!

10. Open the settings of the YouTube addon and go to "API" and select "Enable API Configuration Page" (this was translated by myself, in german it says "API-Einrichtungsseite aktivieren").

11. After enabling that, go with a browser to http://$KODI_IP:50152/youtube/api and fill in the informations.

(thanks to @slax57 from #439 (comment))

12. The last step is to login with the youtube plugin.
    To do so, open the youtube app in kodi and select "Login". There should be a popup telling you to go to google.com/device and enter a code. Unfortunately, i did not make screenshots but it should be very self explanating. After entering the code, i had to enter another code and click on some warnings, because the api has full access. After allowing that, the youtube plugin works again. Thanks @MoojMidge for this great plugin and shame on you youtube for forcing this sh.t.