Github Actions for CI

[Francis Chuang]

A month or so ago, I started a thread on Github Actions on the list. I 
have just replaced Travis with Github Actions for Avatica-Go (CALCITE-3356).

For the workflows in Avatica-Go (currently just 1 for CI), see: 
https://github.com/apache/calcite-avatica-go/tree/master/.github/workflows

The latest run is here: 
https://github.com/apache/calcite-avatica-go/runs/226087805

The VMs provided by Github are a lot beefier (2 core CPUs, 7GB RAM, 14GB 
SSD disk). The tests are slightly slower compare to Travis (in the order 
of seconds), but this is most likely due to us having to check out the 
code during run time and the need to compile the Github Action for 
checking out the code for each run. I don't think this is too much of an 
issue and the direct integration with Github is much nicer.

I think it shouldn't be too difficult to move Avatica and Calcite over. 
We can probably get rid of Appveyor as well since Github Actions 
provides Windows and OS X nodes as well.

One thing that would be interesting would be to move the integration 
tests for Calcite to docker images and run each test for each backend in 
its own job to maximize parallelism and allow each job to maximize the 
available hardware resources.

Francis