Add support for overlays

[mayaCostantini]

Is your feature request related to a problem? Please describe. As a user of the Thoth GitHub action, I would like to have support for different overlays to get security advise on dependencies for multiple environments.

Describe the solution you'd like Support advising on multiple runtime environments

• [x] Link the documentation on how to create a .thoth.yaml configuration file with different overlays and runtime environments
• [x] Add an input parameter to specify an overlay directory
• [x] Document how to create multiple workflows for different runtime environments.

Describe alternatives you've considered Leave the default environment for all recommendations.

[mayaCostantini]

/sig stack-guidance /priority important-soon

[mayaCostantini]

Closed by #32