Implement controllers for API operations

[uniqueg]

This is a meta-issue tracking the progress of the API controller implementation.

When raising PRs to address the individual issues linked below, make sure that for each PR, you:

• add/migrate/update required TES / service info data models (consider using the ones from proTES available here)
• add controller code
• connect available Kubernetes code (originally from tesk-core), but overhaul code and make use of kubernetes wherever possible
• consider addressing legacy issues in TESK, tesk-core and TESK-api, while you are at it
• add unit tests
• make use of TES compliance test suite and the OpenAPI test runner for integration testing
• use typing
• provide Google-style docstrings
• update documentation, if applicable

The following controllers need to be implemented:

• Implement "GET /service-info" operation #157
• Implement "POST /tasks" operation #158
• Implement "GET /tasks" operation #159
• Implement "GET /tasks/{id}" operation #160
• Implement "GET /tasks/{id}:cancel" operation #161

[JaeAeich]

[JaeAeich]

The above diagram is not complete obv but I thought this would be helpful while reviweing #191 #192