title: prisma findUnique where takes only one unique argument
body: <p>I ran into an issue where I need to check if a user exists by his username and email since both are unique fields in the database, but I got an error.
  <code>Argument where of type UserWhereUniqueInput needs exactly one argument, but you provided username and email. Please choose one.</code>
  so, is there a way to execute this query just once?. instead of running one for each like the following</p>
  <pre class="lang-js prettyprint-override"><code>const user = await prisma.user.findUnique({
          where: {
            username,
            email,
          },
        });
  </code></pre>
  <p>and not like this</p>
  <pre class="lang-js prettyprint-override"><code>const user = await prisma.user.findUnique({
          where: {
            username,
          },
        });
  
  const user = await prisma.user.findUnique({
          where: {
            email,
          },
        });
  
  </code></pre>