feat: add direct templates links (#1165)

## Description

Direct templates links is a feature that provides template owners the
ability to allow users to create documents based of their templates.

## General outline

This works by allowing the template owner to configure a "direct
recipient" in the template.

When a user opens the direct link to the template, it will create a flow
where they sign the fields configured by the template owner for the
direct recipient. After these fields are signed the following will
occur:

- A document will be created where the owner is the template owner
- The direct recipient fields will be signed
- The document will be sent to any other recipients configured in the
template
- If there are none the document will be immediately completed

## Notes

There's a custom prisma migration to migrate all documents to have
'DOCUMENT' as the source, then sets the column to required.

---------

Co-authored-by: Lucas Smith <me@lucasjamessmith.me>

packages/lib/utils/templates.ts

@@ -0,0 +1,44 @@
+import type { Recipient } from '@documenso/prisma/client';
+
+import { WEBAPP_BASE_URL } from '../constants/app';
+
+export const formatDirectTemplatePath = (token: string) => {
+  return `${WEBAPP_BASE_URL}/d/${token}`;
+};
+
+/**
+ * Generate a placeholder recipient using an index number.
+ *
+ * May collide with existing recipients.
+ *
+ * Note:
+ * - Update TEMPLATE_RECIPIENT_EMAIL_PLACEHOLDER_REGEX if this is ever changed.
+ * - Update TEMPLATE_RECIPIENT_NAME_PLACEHOLDER_REGEX if this is ever changed.
+ *
+ */
+export const generateRecipientPlaceholder = (index: number) => {
+  return {
+    name: `Recipient ${index}`,
+    email: `recipient.${index}@documenso.com`,
+  };
+};
+
+/**
+ * Generates a placeholder that does not collide with any existing recipients.
+ *
+ * @param currentRecipients The current recipients that exist for a template.
+ */
+export const generateAvaliableRecipientPlaceholder = (currentRecipients: Recipient[]) => {
+  const recipientEmails = currentRecipients.map((recipient) => recipient.email);
+  let recipientPlaceholder = generateRecipientPlaceholder(0);
+
+  for (let i = 1; i <= currentRecipients.length + 1; i++) {
+    recipientPlaceholder = generateRecipientPlaceholder(i);
+
+    if (!recipientEmails.includes(recipientPlaceholder.email)) {
+      return recipientPlaceholder;
+    }
+  }
+
+  return recipientPlaceholder;
+};