support a global `groundhog.toml` config for `hog {init, add}` etc

[OwenPriceSkelly]

Consider the following PEP723 config snippet :

...
# [tool.hog.anvil]
# endpoint = "5aafb4c1-27b2-40d8-a038-a0277611868f"
# account = "cis250461"
# walltime = 300
#
# [tool.hog.anvil.gpu]
# account = "cis250461-gpu"
# qos = "gpu"
# partition = "gpu-debug"
# scheduler_options = "#SBATCH --gpus-per-node=1"
# worker_init = "module load conda"

As a groundhog user who wants to share their script with a colleague, it doesn't make as much sense to have account = "cis250461" tightly coupled to the source code as it does to have e.g. # scheduler_options = "#SBATCH --gpus-per-node=1".

Since some config values might be sensitive and/or user specific, we should allow them to specify a low-precedence default ~/.groundhog.toml like

[tool.hog.anvil]
endpoint = "5aafb4c1-27b2-40d8-a038-a0277611868f"
account = "cis250461"

[tool.hog.anvil.gpu]
account = "cis250461-gpu"

so that the script I share with my colleague only needs the default values that would actually be common to us, not every single option I passed to the executor.

[OwenPriceSkelly]

another option for this which might be more intuitive is to support a --config flag and/or a GROUNDHOG_CONFIG env var which would use the contents of a .toml to just directly populate the script metadata.

the main reason not to do that is that it starts to encourage "projects" of groundhog scripts, which should really just be python packages