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/package.json

@@ -23,6 +23,7 @@
     "test:e2e": "jest --config ./test/jest-e2e.json"
   },
   "dependencies": {
+    "@nestjs-modules/mailer": "^1.8.1",
     "@nestjs/apollo": "^10.1.6",
     "@nestjs/common": "^9.2.1",
     "@nestjs/core": "^9.2.1",
@@ -44,16 +45,17 @@
     "graphql-query-complexity": "^0.12.0",
     "graphql-redis-subscriptions": "^2.5.0",
     "graphql-subscriptions": "^2.0.0",
+    "handlebars": "^4.7.7",
     "io-ts": "^2.2.16",
     "ioredis": "^5.2.4",
     "luxon": "^3.2.1",
+    "nodemailer": "^6.9.1",
     "passport": "^0.6.0",
     "passport-github2": "^0.1.12",
     "passport-google-oauth20": "^2.0.0",
     "passport-jwt": "^4.0.1",
     "passport-local": "^1.0.0",
     "passport-microsoft": "^1.0.0",
-    "postmark": "^3.0.15",
     "prisma": "^4.7.1",
     "reflect-metadata": "^0.1.13",
     "rimraf": "^3.0.2",
@@ -72,6 +74,7 @@
     "@types/jest": "^29.4.0",
     "@types/luxon": "^3.2.0",
     "@types/node": "^18.11.10",
+    "@types/nodemailer": "^6.4.7",
     "@types/passport-github2": "^1.2.5",
     "@types/passport-google-oauth20": "^2.0.11",
     "@types/passport-jwt": "^3.0.8",