[FR] Adding global var

[EhyMaik97]

I'm always frustrated when I see line repeated. In the /snippets/database/index.py there are 4 times the string "https://databaseName.firebaseio.com"

I want to substitute four equals string with an env var like DB_URL and insert the string above, so in this way the user have to edit it only 1 time

[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.