Integrate CLI arguments with `djls-conf` settings

[joshuadavidthomas]

Integrate CLI arguments into the configuration loading handled by the djls-conf crate, allowing CLI flags to override settings found in files.

This came up while working on #66, but I punted it because merging CLI arguments with the settings loaded by the config crate (which djls-conf uses) can be a bit tricky.

The desired priority for settings is:

1. CLI Arguments
2. Project Files (djls.toml, .djls.toml, pyproject.toml)
3. User Config File (~/.config/djls/djls.toml)
4. Defaults

To do this, we'll need to map the CLI arguments to the fields in the Settings struct within djls-conf and decide where in the startup sequence this merge should happen.