Introduce an API layer for GithHub authentication and managing tokens

[karpikpl]

This is by not any means ideal but wanted to share an idea for managing tokens and authentication so that dashboard could be deployed.

I'm open to discussion. I think ideally the solution supports all 3 options:

1. mocked data
2. personal access tokens
3. GitHub App authentication

I could include the PAT token into the API layer and skip the auth flow when present - just store it in session.

The only thing remaining in this PR is:

1. Decide if we want to go with one docker file (for backend/frontend) or two (one frontend - current solution and another one for backend/frontend)
2. Automatically copy "dist" to API project for local development