Choose “All Applications” (or you can specify and individual application, like Mail, if you prefer)
Enter “Paste and Match Style” (enter it exactly as is. It’s not asking you make up a name–it’s asking you for the exact name of the existing menu command)
Press “Command + V” (or whatever shortcut you want to use). That will capture the new shortcut. Command + V will override the regular paste command. You can also specify a different keyboard shortcut if you’d like to have the option of both.