set up gitbub actions ci

[Tao Wu <wu...@gmail.com>]

Hi, everybody,

I've set up CI on Github Actions for XiaoMi/rdsn [1], which previously ran
CI on travis-ci.

Since our CI includes time-consuming compilation, the limited resources on
travis-ci are unsatisfiable to us. A CI task usually spends 40+ mins to
finish.

Now this problem is resolved. Github Actions significantly reduces our CI
time, we are able to run a job matrix with more sophisticated testing, with
clang and sanitizers.

Some notes on Pegasus CI on Github Actions are given in this wiki:
https://cwiki.apache.org/confluence/display/PEGASUS/Github+Actions. We may
continue to merge the rdsn/ into pegasus/. And after that,
the incubator-pegasus project will use Github Actions as well.