Use Github Actions for CI

[mlarraz]

Also drop support for older Ruby and Rails versions.

Todo:

• Support for newer Ruby and Rails versions
• Support for Cassandra 4.x
• Update and fix Rubocop

Sample run: https://github.com/mlarraz/cequel/actions/runs/2234553912

This won't run on the parent repo until it's merged

[mlarraz]

@ilanusse @pezra would appreciate any attention this can get so this project can get revitalized if possible

[noedlm]

@ilanusse @pezra we have a rails project that uses Cassandra. Is there any update on the status of this and any relevant gems? Are they pretty much dead, someone else planning on updating/maintaining it?