Allow running cargo xtask sdb to take an additional argument for custom database.

[AldaronLau]

Is your feature request related to a problem? Please describe.
Some people have expressed interest in wanting to create mappings without committing them to this repository.

Describe the solution you'd like
They should be able to build a TOML file and use cargo xtask sdb /path/to/my/database to generate the bytecode file.

Describe alternatives you've considered
A GUI could do this automatically.

Additional context
TODO: Add any other context or screenshots about the feature request here.