refactor: update mailer service to stop using postmark (#38)

* refactor: update mailer service to stop using postmark

* chore: remove postmark as a dep and move out postmark code

* chore: remove postmark variables from .env.example

* chore: add formal errors for mailer initialization errors

* chore: add and update jsdoc comments in mailer service methods

packages/hoppscotch-backend/src/mailer/mailer.module.ts

@@ -1,7 +1,29 @@
 import { Module } from '@nestjs/common';
+import { MailerModule as NestMailerModule } from '@nestjs-modules/mailer';
+import { HandlebarsAdapter } from '@nestjs-modules/mailer/dist/adapters/handlebars.adapter';
 import { MailerService } from './mailer.service';
+import { throwErr } from 'src/utils';
+import {
+  MAILER_FROM_ADDRESS_UNDEFINED,
+  MAILER_SMTP_URL_UNDEFINED,
+} from 'src/errors';
 
 @Module({
+  imports: [
+    NestMailerModule.forRoot({
+      transport:
+        process.env.MAILER_SMTP_URL ?? throwErr(MAILER_SMTP_URL_UNDEFINED),
+      defaults: {
+        from:
+          process.env.MAILER_ADDRESS_FROM ??
+          throwErr(MAILER_FROM_ADDRESS_UNDEFINED),
+      },
+      template: {
+        dir: __dirname + '/templates',
+        adapter: new HandlebarsAdapter(),
+      },
+    }),
+  ],
   providers: [MailerService],
   exports: [MailerService],
 })