API: Provide project links info (eg github url, trello url etc.)

[lululeon]

Related to #2

This ticket is to ensure the api can provide the project's links / urls (e.g. to services such as github, trello, jira etc). The implementation should be forward-looking so that a set of links can be stored per project.

⚠️ Future auth requirements will mean these will only be surfaced for the project owner (and potentially team-members). For now, the route handler should assume it can only return a string (instead of a url) that describes the 3rd party integration. (e.g. https://github.com/someUser/someRepo becomes github).

Acceptance criteria

• updates to data/sample.json to include sufficient data & relationships for describing a project's "tech stack"
• updates to the api yaml spec / addition plus any needed entities in the api components block
• updates to route handler(s) logic as needed
• addition of passing tests for introduced route(s)