Add CI/CD

[oubiwann]

Does Gitub Actions support Erlang yet? If so, great. If not, set up for Travis CI ...

• [x] Add config(s) for CI/CD infra
• [x] Add badges to README to indicate build status
• [x] Add support for testing against multiple versions of Erlang
• [x] Explore ways of testing the plugin commands in CI/CD jobs

[oubiwann]

Github Actions does support Erlang; testing it out now ...

[oubiwann]

Verified as running successfully.