Extensions for rendering & UI

[davidmehren]

We should discuss if we ever want to support some form of official extensibility for the client. There were two requests relating to that in the past:

• https://github.com/hedgedoc/hedgedoc/issues/569 asks for custom editor buttons. I would add to the request custom buttons/links in the navbar, e.g. to link to the homepage of the organization.
• https://github.com/hedgedoc/hedgedoc/issues/20 asked for extensions of the rendering process. We already have that issue in this repo as https://github.com/hedgedoc/react-client/issues/438, which got merged into https://github.com/hedgedoc/react-client/issues/360. But #360 only talks about an internal system. What about external plugins?

[mrdrogdrog]

It's not impossible but also definitely not easy, because:

• we have to generalize a lot of code, write docs, prevent security issues and bugs.
• if we create a public extension api, then we definitely will get issues that are related to plugins.
• Because our frontend is webpacked, I'm sure you'll have to compile the frontend yourself (and therefore also e.g. the docker container) to include plugins.

[DerMolly]

An internal extension api is implemented see #360, but we don't have any plans to make it publicly available. Therefore this issue will be closed.