CircleCi to Github actions migration

[souzamari]

This PR migrates existing CircleCI workflow of optable-ios-sdk to GitHub actions

The runners needed to be updated and we can't use the same runner for setup and for build:

• for setup we must use macos-13 otherwise the ruby version is unavailable. If the dependencies are cached it won't fail with macos-14, but we should not rely on the cache.
• for building we must use macos-14, otherwise the build will fail

The CircleCI workflow ran in 2 different cases:

• pull-request runs the tests, build-demo-swift and build-demo-objc: jobs for the standard build
• tagging with vX.Y.Z runs the tests, build-demo-swift, build-demo-objc: and success-slack-notify

Slack notifications will be added back eventually when a reusable action is created, for now we're ignoring it as it's not a critical part of the build process.

The workflow is essentially the same for pull-requests and tagging, for the sake of simplicity we are using the same workflow in the github action, eventually it could be split in 2. Contrary to the web-sdk, the publishing step needs to be done manually and the process is described in the releasing.md file.

The only artifact that was published with CircleCi was the build log

This github action creates the following artifacts:

• test output
• the pods for each demo
• the build log for each demo

Slack integration notification:

[Yoshiji]

neat 👌