Shell tab completion now available for Zsh and Fish

Batect now supports shell tab completion in both Zsh and Fish.

This supports both options (eg. ./batect --outTab completes to ./batect --output) and task names (eg. ./batect bTab completes to ./batect build):

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To get started, update your project to Batect 0.68.0, then follow the installation instructions for your shell.