feat(email): integrate html-to-text for email body conversion

- Added `html-to-text` package to convert HTML email bodies to plain text alternatives.
- Updated `EmailService` to handle HTML content in emails, ensuring both HTML and plain text formats are sent.
- Enhanced unit tests to verify the new email sending behavior with HTML content.

Author: jzunigax2

package-lock.json

@@ -46,6 +46,7 @@
     "cross-env": "^10.1.0",
     "dayjs": "^1.11.20",
     "helmet": "^8.1.0",
+    "html-to-text": "^10.0.0",
     "internxt-crypto": "^1.5.0",
     "ioredis": "^5.10.1",
     "nanoid": "^5.1.5",
@@ -73,6 +74,7 @@
     "@swc/core": "^1.15.18",
     "@types/chance": "^1.1.7",
     "@types/express": "^5.0.6",
+    "@types/html-to-text": "^9.0.4",
     "@types/multer": "^2.1.0",
     "@types/node": "^22.15.0",
     "@types/nodemailer": "^8.0.0",