[feature] support local configuration

[gomain]

My particular use case is that I want to organize directories such that exercism exercises are stored under different local directories for different tracks.

learning/
  rust/
    exercism/ # rust exercises go here
  haskell/
    exercism/ # haskell exercises go here

Perhaps a flag -l, --local where configurations are stored in a .exercism/ directory in the current directory. And that the exercism command searches up the directory tree merging configurations giving precedence to closer configurations.

Such that I can do

[rust]$ exercism configure --local --workspace ./exercism

[github-actions]

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