ci: shell installer via dist

[lwshang]

SDK-2459

Sample release: https://github.com/dfinity/icp-cli/releases/tag/dist%2F0.1.0-beta.3

The shell installer & updater are included in the release.

$ curl --proto '=https' --tlsv1.2 -LsSf https://github.com/dfinity/icp-cli/releases/download/dist/0.1.0-beta.3/icp-cli-installer.sh | sh
downloading icp-cli 0.1.0-beta.3 x86_64-unknown-linux-gnu
installing to /home/lwshang/.cargo/bin
  icp
  icp-cli-update
everything's installed!

The dist tool required that the tag matches the version in Cargo.toml. So the version overwriting logic (env var ICP_CLI_VERSION) in build.rs is removed and the version is bumped to v0.1.0-beta.3.