Automate this repository with GitHub Actions

[viral32111]

Proposed changes

• Use GitHub actions to run a GLua Linter to verify and check code from pushed commits.
• Use GitHub actions to automate releases by automatically compressing the addon to a .gma.

Explanation

GitHub actions allows for command-line tasks to be ran whenever events such as pushes, pull requests, new issues, drafted releases, etc, happen on the repository. There are many other addons on GitHub that already use FPtje's GLua Linter to analyise and check code that gets pushed. Whenever code containing errors is commited/pushed, GitHub actions will automatically notify the commit author and repository contributors.

To take the effort off us for compressing addon content so it's ready for the workshop, we can use GitHub actions bundled with GMad to automatically generate a .gma file whenever a new release is drafted. Meaning all we have to do is write the highlights and upload the changes to the Steam Workshop. Thankfully, this process has also been changed with the new ISteamUGC system in-place. Only content that's been changed on the .gma file has to be uploaded, so no longer do we have to upload the whole 2GB for every single update.