Add first GitHub entities and automatically fetch them for the leaderboard

[GODrums]

Motivation

To make our Leaderboard possible, we first have to fetch the required PRs / Comments data from Github's API and store them in the database, as well as make the data available through our own API.

Description

• Adds application-local.yml-support for the Github PAT
• Adds the database structure for Github's API/Webhook schema
• Provides a sample runner to store Hephaestus`s data in the database
• Provides a Github API Client + GraphQL Client as fallback

Next up for the leaderboard (in other PRs):

• Webhook integrations (NATS)
• More endpoints depending on which data we need in our front-end

Screenshots (if applicable)

Checklist

General

• PR title is clear and descriptive
• PR description explains the purpose and changes
• Code follows project coding standards
• Self-review of the code has been done
• Changes have been tested locally
• Screenshots have been attached (if applicable)
• Documentation has been updated (if applicable)

Server (if applicable)

• Code is performant and follows best practices
• No security vulnerabilities introduced
• Proper error handling has been implemented
• Added tests for new functionality
• Changes have been tested in different environments (if applicable)

[FelixTJDietrich]

I did not look at everything, but some comments also apply to the other files. Let's do this PR right and set the standard for future PRs :) Also as reference.

[FelixTJDietrich]

Some more final comments

[FelixTJDietrich]

I think the code looks good now, maybe you can take a quick look at ResponseEntity and the returned NotFoundException. Also you need to update the angular API client library, there is a command that you need to run in package.json. Afterwards we can merge this PR :)

[FelixTJDietrich]

I have only a minor comment, the rest looks fine. You still need to make the checks pass.

[FelixTJDietrich]

Code LGTM now, thank you!