[Feature]: Make location of configuration file configurable

[neubig]

What problem or use case are you trying to solve?

Currently OpenHands, by default, loads config.toml from the base directory of the repository. However, if we have a single OpenHands installation that is used by multiple users, or we wanted to use OpenHands as a library, this behavior may be too rigid.

Describe the UX of the solution you'd like

It should be possible to specify the location of the config.toml file by adding an argument to the load_app_config() function in openhands/core/config.py, and then modify all command line programs that call load_app_config() so that they take in an argument that can optionally specify the location of the config.toml file.