Updates the Supabase template to include an default edge.yaml file.

[dshukertjr]

Currently the default Supabase project doesn't include an edge.yaml file by default, and the developers have to create it manually. This PR adds a default edge.yaml file. Also, the configuration key on the edge.yaml file didn't work with camel case, but instead works with snake case, so updated the docs.

Fixes https://github.com/invertase/dart_edge/issues/36, https://github.com/invertase/dart_edge/issues/59, https://github.com/invertase/dart_edge/issues/58, https://github.com/invertase/dart_edge/issues/52

[CLAassistant]

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