Add GitHub Actions workflow that generates pdf file automatically

[horror-proton]

This workflow will be triggered on pushes to master and all pull requests, it would build and then upload a pdf file to artifacts automatically. Which allows readers to download latest draft of pdf file directory from GitHub.

Limitations: some of the fonts in ctex-fontset-my.def are not quite available (copyright issue), so pdf files generated will be using fandol as fontset.

Here is an example