Auto-generate API documentation with each commit to master using Github Actions

[diptorupd]

Currently, I have been updating the API docs for dpctl by manually generating and pushing the documents to the gh-pages branch. The steps that I use are:

Step 1

git checkout master
cd docs
mkdir build
cd build 
cmake -DDPCTL_DOCGEN_PREFIX=<Some location out of tree>
make Sphinx

Step 2

git clean -dfx
git checkout gh-pages
git rm -rf *
mv <Location where docs were generated in first step> .
git ci -m "Updated docs."
git push

We should be able to do these using Azure as part of CI.