Move join existing call modal

src/home/JoinExistingCallModal.jsx

@@ -0,0 +1,19 @@
+import React from "react";
+import { Modal, ModalContent } from "../Modal";
+import { Button } from "../button";
+import { FieldRow } from "../Input";
+import styles from "./JoinExistingCallModal.module.css";
+
+export function JoinExistingCallModal({ onJoin, ...rest }) {
+  return (
+    <Modal title="Join existing call?" isDismissable {...rest}>
+      <ModalContent>
+        <p>This call already exists, would you like to join?</p>
+        <FieldRow rightAlign className={styles.buttons}>
+          <Button onPress={rest.onClose}>No</Button>
+          <Button onPress={onJoin}>Yes, join call</Button>
+        </FieldRow>
+      </ModalContent>
+    </Modal>
+  );
+}