Publish `@finos/git-proxy-cli` to npm, check quickstart guide accuracy

[jescalada]

@finos/git-proxy-cli has never been published to NPM. Meanwhile, both the installation docs and the quickstart approval walkthrough tell users to install and run it, so those commands fail with a 404.

Prior to 2.0.0 (last verified version is 2.0.0-rc.5), @finos/git-proxy shipped on NPM with the package/git-proxy-cli included. We started shipping just the dist folder instead of the whole source, however CLI publishing wasn't set up to allow users to access CLI directly.

Broken commands in the docs

• docs/installation: npm install -g @finos/git-proxy-cli
• docs/installation: npm install -g @finos/git-proxy-cli@1.0.0 (version never existed)
• docs/quickstart/approve: npx -- @finos/git-proxy-cli login --username admin --password admin

Describe the solution you'd like

packages/git-proxy-cli/package.json on main is already good to publish, only the release workflow is missing.

Additional context
Discussion in #1652 where we realized something was wrong

Blocked by

#1520 and #1627, both touching our release process.