feat(links): Added links api for backend processing

[benjackwhite]

Problem

Bored on a flight and wanted to see if we could get the existing hog function logic to work for links.

Part 1 is just to make links work in a basic way. Part 2 would be to have a related hog function that can be used for processing the link (e.g. custom tracking, custom redirection etc.)

Changes

• Sets up new service
• Adds hog function processing

Follow up

• Setup short domain to point to our service
• Rewrite path to the sub api

How did you test this code?

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

Changelog: (features only) Is this feature complete?

[posthog-bot]

This PR hasn't seen activity in a week! Should it be merged, closed, or further worked on? If you want to keep it open, post a comment or remove the stale label – otherwise this will be closed in another week. If you want to permanentely keep it open, use the waiting label.