Create a test suite and setup ci to run them

[jneira]

• We are suffering from several bugs lately which mase us do subsequent bugfix releases
• So final users are effectively testing the extension hitting bugs directly, That is very very bad experience.
• We need urgently a test suite to prevent this
• In the meanwhile we will be more strict with manual testing of pr's, verifying them ourselves

[jneira]

• Info about integration tests over vscode extensions:
  • https://code.visualstudio.com/api/working-with-extensions/testing-extension
  • https://github.com/microsoft/vscode-test
  • https://github.com/microsoft/vscode/tree/main/extensions/vscode-api-tests: to discover the vscode api and how to test it at same time
  • testing setup from the java extension: https://github.com/redhat-developer/vscode-java/blob/master/test
  • testing setup from the official python extension: https://github.com/microsoft/vscode-python/tree/main/src/test