Use CI/CD workflow for building pull requests

[wborn]

The CI/CD GitHub Actions workflow should also be used for building PRs so we know that the code keeps compiling when PR changes are merged.

[Miggets7]

@wborn this is already happening I think? Or is something else needed?

[wborn]

It doesn't use it for PRs yet. The on.pull_request event (see openremote/openremote) is missing.

It's probably best to first make CI/CD build successfully (#22) otherwise the PR build status will just be ignored. Using fastlane might simplify building/publishing the iOS/Android apps.