fix: support dynamic external ids for direct templates (#1274)

Adds support for an `externalId` query param to be passed when linking a
user to a direct template. This external id will then be stored on the
document upon signing completion.

packages/trpc/server/template-router/router.ts

@@ -66,6 +66,7 @@ export const templateRouter = router({
           directRecipientName,
           directRecipientEmail,
           directTemplateToken,
+          directTemplateExternalId,
           signedFieldValues,
           templateUpdatedAt,
         } = input;
@@ -76,6 +77,7 @@ export const templateRouter = router({
           directRecipientName,
           directRecipientEmail,
           directTemplateToken,
+          directTemplateExternalId,
           signedFieldValues,
           templateUpdatedAt,
           user: ctx.user