[AI] Integrate Image-to-Image tasks for a generic image-to-image pipeline

[RUFFY-369]

What does this pull request do? Explain your changes. (required)

Adds support for the ai-worker pipeline which integrates image-to-image tasks into a generic framework. The current tasks in the generic frameworks include inpainting, outpainting and sketch-to-image

Corresponding AI-Worker PR: livepeer/ai-worker#388

Specific updates (required)

• removes requirement of creating a separate pipeline for a specific task for eg., three different pipelines were required for the above mentioned tasks in the current scheme of things. This PR works on creating a generic framework for specific input-output pipeline where user can perform various tasks in that single pipeline itself by specifying the task parameter
• Adds inpainting, outpainting and sketch-to-image as tasks in a single I2I generic pipeline

How did you test each of these updates (required)
Test was performed by running the gateway + worker locally.

Does this pull request close any open issues?

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

cc @rickstaa