Change DB filename according to Rocket environment

Rocket.toml

[global]
template_dir = "static"


# equivalent to
# [global.databases.sqlite_database]
# url = "db/db.sqlite"

[development]
databases = { sqlite_database = {url = "db/dev.sqlite" } }

[staging]
databases = { sqlite_database = {url = "db/staging.sqlite" } }