Implement confirm user functionality

This commit adds the necessary functionality to confirm a user's account.

It includes the addition of a new column in the user table to track whether an account is confirmed or not, and the implementation of JWT for confirmation tokens.

This commit integrates the SparkPost API as well as React Email to send dynamic emails for whatever purpose.

Upon user registration, a confirmation email will be sent to the user.

emails/Welcome.tsx

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+import { Container, Heading, Text, Button, Section } from '@react-email/components';
+import { Tailwind } from '@react-email/tailwind';
+
+import { FC } from 'react';
+
+interface WelcomeEmail {
+  subject?: string;
+  name?: string;
+  url?: string;
+}
+
+const Welcome: FC<WelcomeEmail> = ({ name, url }) => (
+  <Tailwind>
+    <Container className="flex h-full w-full flex-col items-center justify-center">
+      <Section>
+        <Heading className="text-2xl font-bold">Welcome to The Biergarten App!</Heading>
+
+        <Text>
+          Hi {name}, welcome to The Biergarten App! We are excited to have you as a member
+          of our community.
+        </Text>
+
+        <Text>
+          The Biergarten App is a social network for beer lovers. Here you can share your
+          favorite beers with the community, and discover new ones. You can also create
+          your own beer list, and share it with your friends.
+        </Text>
+
+        <Text>
+          To get started, please verify your email address by clicking the button below.
+          Once you do so, you will be able to create your profile and start sharing your
+          favorite beers with the community.
+        </Text>
+
+        <Button href={url}>Verify Email</Button>
+
+        <Text className="italic">
+          Please note that this email was automatically generated, and we kindly ask you
+          not to reply to it.
+        </Text>
+      </Section>
+    </Container>
+  </Tailwind>
+);
+
+export default Welcome;