ci: release workflow updates

[armcknight]

• removed xcbeautify because it was dropping some vital logs on the floor. oh well, builds get faster anyways without having to install it
• removed the make release task and just inlined that logic in deploy_project.sh. the extra indirection was annoying
• set up to use the actions secrets for CI
• updated release section of readme to describe how it works now

You can see a successful build here: https://github.com/sentry-demos/ios/actions/runs/6413830753/job/17413303661