Bring install.ps1 to functional parity of install.sh

[sanfrancrisko]

As part of the release prep for 0.5.0, the install.sh script was enhanced to:

• Fetch the releases checksums file (e.g. 0.4.0 checksums.txt)
• Wrap all curl commands in a retry loop, to improve reliability in CI runs, as it was observed that the macos-latest and ubuntu-latest runners would occasionally fail to install PCT because of a 404 from Github
• Split up each URI GET to Github and check the response code
• Output more debug logging (enabled via the PCT_INSTALL_DEBUG env var) to help us diagnose / investigate failures on CI runs

The install.ps1 was not enhanced at the time, as it was proving to be more reliable, however, we should not have as big a functional difference between them and should look to implement the above enhancements in install.ps1 too.