Github Actions - Unit and Integration tests

[Lirt]

Closes https://github.com/Lirt/velero-plugin-for-openstack/issues/44

Scenarios:

• [x] Execute unit tests
• [x] Install Kind, Velero, Velero-CLI, Devstack
• [x] Build docker image and load it to kind
• [ ] Install Cinder-CSI-Plugin
• [x] Execute simple test backup
• [x] Execute simple test restore
• [ ] Execute test backup with volume
• [ ] Execute test restore with volume

Signed-off-by: Ondrej Vasko ondrej.vaskoo@gmail.com

[Lirt]

Some scenarios will be postponed for future MRs as they require more troubleshooting time to properly configure:

• [ ] Install Cinder-CSI-Plugin
• [ ] Execute test backup with volume
• [ ] Execute test restore with volume

Basic tests which were implemented in this MR will already help a lot to catch most fundamental errors.