Scripts field to spawn a command from Aliae itself

[RuiNtD]

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What would you like to see changed/added?

It be would nice to have a spawn field on Scripts, that has aliae itself spawn a process. Main use-case would be for Nushell:

- if: match .Shell "nu"
  spawn: oh-my-posh init nu
  value: source ~/.oh-my-posh.nu

For nu, putting both of these commands into value (which is actually shown in docs) is actually incorrect syntax, since source is handled at parse and doesn't simply act as an "eval", so it just execs the results of the last oh-my-posh init nu if done that way.