feat: Support Environment Variables for Hook Commands

[TekWizely]

Adds ability to configure environment variables to be set when invoking hook commands. Variables are configured via hook "args" using the following argument pattern:

--hook:env:NAME=VALUE

feat: Add support for "--hook:error-on-output" in my-cmd-* hooks.

• Can exist anywhere in the arg list before a '--' argument
• re: Support for plain '--error-on-output' at first element
  • Still works (currently)
  • Is now deprecated and will be removed in a future version

chore: Use "/usr/bin/env" to invoke commands

• No-longer invokes the commands directly
• Makes it trivial to pass environment variables to commands
• Should not cause issues as /usr/bin/env was already vital

chore: Add "shellcheck source" declarations on dynamically sourced files

• Only files that were already modified for this PR were addressed

Breaking Change: For compatibility with file-based hooks, Repo-based hooks no-longer ignore '--', or proceeding arguments, in the argument list. However, to further match file-based logic, the first '--' will be consumed, treating anything after it as OPTIONS to be passed to the hook command.

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TODOS:

• [ ] Update Docs

replaces #25

cc: @timuralp