[#2161] One-Stop Config File for Code Portfolio

[lyuanww]

Part of #2161

Proposed commit message

Implement One-Stop Config File for Code Portfolio.

Currently, `report-config.json` is underutilised (it is only used for
defining report titles). However, considering the code portfolio
feature, we need to implement a config file that allows users to
quickly set up and deploy it to their favourite platform to host
websites.

Let's move to repurpose `report-config.json` into a YAML file that
users can use it to set up configs to build their code portfolio more
easily.

• Implement MVP version from previous PR
• Handle optional fields and error handling
• Add filesizelimit field
• Implement blurb overriding priority
• Implement configuration overriding priority logic
• Refactor default instances out of some classes
• Fix and add tests for code coverage
• Update docs

Behaviour

Configuration files priority:
CLI (--repos flag) -> new YAML file (if present and correctly formatted and repos section present) -> CSV files

Blurbs priority:
Take blurbs either from blurbs field in YAML file or from blurbs.md. If both present, take the one in blurbs.md.

Credit

Referenced and branched off from #2192