feat(macos): build a signed .app bundle in a .dmg

[andygrundman]

Description

This PR should be able to build a signed or unsigned Sunshine.app from both CI and from a manual build script. 6 secrets are required to properly sign and notarize a Mac app. Since CI produces builds from pull requests containing unknown code, I took care to only automatically sign builds when github.event_name == push.

An unsigned build should be possible to run but requires jumping through a few security hoops: "Open Anyway" as well as possibly forcing the removal of the quarantine bit.

The .app bundles all dependent libraries in the Frameworks directory, as well as all web UI assets in the Resources directory, so everything should be fully self-contained.

I don't think it breaks any other build including Mac homebrew, but it's difficult to test all possible CI builds as some appear to require various secrets.

Screenshot

Issues Fixed or Closed

• Resolves https://github.com/orgs/LizardByte/discussions/547

Roadmap Issues

• Closes Sunshine: Create macOS dmg package roadmap#18

Type of Change

• feat: New feature (non-breaking change which adds functionality)
• fix: Bug fix (non-breaking change which fixes an issue)
• docs: Documentation only changes
• style: Changes that do not affect the meaning of the code (white-space, formatting, missing semicolons, etc.)
• refactor: Code change that neither fixes a bug nor adds a feature
• perf: Code change that improves performance
• test: Adding missing tests or correcting existing tests
• build: Changes that affect the build system or external dependencies
• ci: Changes to CI configuration files and scripts
• chore: Other changes that don't modify src or test files
• revert: Reverts a previous commit
• BREAKING CHANGE: Introduces a breaking change (can be combined with any type above)

Checklist

• Code follows the style guidelines of this project
• Code has been self-reviewed
• Code has been commented, particularly in hard-to-understand areas
• Code docstring/documentation-blocks for new or existing methods/components have been added or updated
• Unit tests have been added or updated for any new or modified functionality

AI Usage

• None: No AI tools were used in creating this PR
• Light: AI provided minor assistance (formatting, simple suggestions)
• Moderate: AI helped with code generation or debugging specific parts
• Heavy: AI generated most or all of the code changes