Replace multiple CLI options with a single --config-file option

[mdpiper]

The bmi-topography CLI includes the following options for configuring a call to the OpenTopography REST API:

• dem_type
• south
• north
• west
• east
• output_format

It's cumbersome to set all of these options. The CLI would easier to use and script if values for these options were instead placed in a text configuration file (e.g., yaml or toml), then referenced with an option such as --config-file.

[mdpiper]

The above is from a suggestion by @mcflugen. He also suggests hardcoding the name of the config file; e.g., it must be named bmi-toppography.toml.