JWT refresh tokens

Per @BowlingX:

> I implemented it, although I would say this is out of scope of postgraphile. I'm using an apollo middleware to detect expired JWT tokens, then I refresh the token and replay the request (this way the user does not realize anything)
I'm using keycloak as my identity management and just have a verification middleware in front of postgraphile (as explained in the docs)
I use passport-oauth2-refresh on nodejs side
https://gist.github.com/BowlingX/356e6cdf071aeee97f842dd9e12d5c53
>
> Then I have this error handler in apollo on ssr side: https://gist.github.com/BowlingX/33ab1c448f6b635769083aece1ba875d
>
> And this one on the frontend error link: https://gist.github.com/BowlingX/1a9d7971bb31b4aab70680ab5a067e6b

-- https://discordapp.com/channels/489127045289476126/498852330754801666/678953091839819777

@BowlingX plans to write an example app or guide for the website

Start with the three linked gist examples and the website's documentation entry points; compare the middleware, SSR error handler, and frontend error link flow described there. Done means adding the promised example app or guide covering the Keycloak and Node.js JWT refresh-token setup.

Written by the indexing model from the issue text.