Update obs-plugintemplate to match changes on obs-studio master

[PatTheMav]

Description

Updates the plugintemplate to support changes and new features of obs-studio on master, most importantly including support for Qt6 and the most recent dependencies.

Motivation and Context

Enable plugin developers to migrate their current plugins to:

• Build out-of-tree by default
• Use Qt6
• Build with Apple Silicon support on macOS
• Codesign and notarize (if possible) on CI

How Has This Been Tested?

Build and packaged the plugintemplate on macOS 12.5, Windows 11, and Ubuntu 22.

Types of changes

• Bug fix (non-breaking change which fixes an issue) New feature (non-breaking change which adds functionality)

Checklist:

• [x] My code has been run through clang-format.
• [x] I have read the contributing document.
• [x] My code is not on the master branch.
• [x] The code has been tested.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] I have included updates to all appropriate documentation.