feat(sltt-app): sign and notarize macos application

[Nathan22Miles]

What issue(s) is this trying to resolve?

• feat(sltt-app): Sign and notarize Mac application #9

How does it all work?

• In order for a Mac application to be successfully installed, the app installer must be signed (with a certificate) and notarized (uploaded to Apple to be scanned for viruses, etc.).

What particularly has changed?

• Description of procedure HERE
• Signing certificate created
• .env file with notarization credentials created
• package.json "build" object updated with Mac build config

Steps for testing

1. yarn build:mac
2. Copy newly created .dmg file to another mac
3. Launch dmg file, drag application icon to Applications folder, launch application, smoke test.

ticket: https://github.com/ubsicap/sltt-app/issues/9 commit-convention: https://www.conventionalcommits.org/en/v1.0.0/