## What
This PR removes or updates references in the docs to Heroku. Most of the code samples have been replaced with a more generic `unleash.example.com` url, while other references have been removed or updated.
Also removes old OpenAPI files that are out of date and redundant with the new generation.
## Background
Come November and Heroku will no longer offer free deployments of Unleash, so it's about time we remove that claim.
Links to the heroku instance are also outdated because we don't have that instance running anymore.
Finally, the OpenAPI files we do have there are old and static, so they don't match the current reality.
## Commits
* Meta: update ignore file to ignore autogenerated docs
I must've missed the ignore file when looking for patterns.
* docs: delete old openapi file.
This seems to have been a holdover from 2020 and is probably
hand-written. It has been superseded by the new autogenerated OpenAPI docs.
* docs: add notes for heroku changes to the frontend readme and pkg
* docs: remove old openapi article and add redirects to new openapi
* docs: fix link in overview doc: point to GitHub instead of heroku
* docs: update quickstart docs with new heroku details
* docs: remove reference to crashing heroku instance
* docs: remove references to herokuapp in code samples
* docs: add a placeholder comment
* docs: update references for heroku updates
* docs: keep using unleash4 for enterprise
* docs: remove start:heroku script in favor of start:sandbox
* docs: remove 'deploy on heroku button'
Now that it's not free anymore (or won't be very shortly), let's
remove it.
* docs: remove extra newline
## What
This PR fixes some broken links that have been hanging around in the
docs for what seems like a very long time.
## Why
As discovered by the link check in #1912, there are a fair few broken
links in the docs. Everyone hates broken links because it makes it
harder to understand what they were supposed to be pointing at.
## How
There are 3 types of links that have been fixed:
- Links that should have been internal but were absolute. E.g.
`https://docs.getunleash.io/path/article` that should have been
`./article.md`
- External links that have changed, such as Slack's API description
- GitHub links to files that either no longer exist or that have been
moved. These links generally pointed to `master`/`main`, meaning
they are subject to change. They have been replaced with permalinks
pointing to specific commits.
-----
* docs: fix slack api doc link
* docs: update links in migration guide
* docs: fix broken link to ancient feature schema validation
* docs: update links to v3 auth hooks
* docs: update broken link in the go sdk article
* Fix: use permalink for GitHub link
* docs: fix wrong google auth link
