fix(install): fix install script crashing when run on Windows with Git Bash

[bdngeorge]

Summary

Closes #1736.

• Adds support for using the install.sh script when on Git Bash.
• Scans for Windows as OS
  • Adds .exe to the binary name
  • Uses .zip instead of .tar.gz
    • Uses unzip command instead of tar command
• Updates README.md (all languages) and INSTALL.md
• Builds out tests for install script using existing test-install.sh file
  • Doesn't add to CI pipeline, wasn't there before

Test plan

• cargo fmt --all && cargo clippy --all-targets && cargo test
• Manual testing: rtk <command> output inspected
• Updated test-install.sh and ran manually

Important: All PRs must target the develop branch (not master).
See CONTRIBUTING.md for details.

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