Add a configuration file for GitHub Actions

Add a configuration file for GitHub Actions

Add a workflow file for GitHub Actions, with jobs that build and test
e2fsprogs on various platforms with various options.

The workflow is configured to run on pushes only, since e2fsprogs does
not use GitHub pull requests.

This will work on any e2fsprogs fork on Github that has GitHub Actions
enabled.  For example, the results for the testing I've been doing are
at https://github.com/ebiggers/e2fsprogs/actions.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>