Add DB environment variables to appwrite-worker-mails

[mbackonja]

What does this PR do?

I found a similar issue and PR like this for such an error but on webhooks worker container...
webhooks container issue: #7844
PR for that issue: #7848

The same error is happening on mails worker

Fixes: #8001

Test Plan

After installing the version from my PR, I can observe in docker-compose.yml in appwrite directory that service named appwrite-worker-mails now contains

      - _APP_DB_HOST
      - _APP_DB_PORT
      - _APP_DB_SCHEMA
      - _APP_DB_USER
      - _APP_DB_PASS

Also after sending the invite, I got no errors while watching logs of appwrite-worker-mails container

Related PRs and Issues

• 🐛 Bug Report: Failed to create connection in appwrite-worker-mails container #8001

Checklist

• Have you read the Contributing Guidelines on issues?
• If the PR includes a change to an API's metadata (desc, label, params, etc.), does it also include updated API specs and example docs?