We weren't doing it before because we weren't starting the plugins.
Now we are.
The hardest part of this was handling the files the tests expect
to be on the filesystem. extraConfigFiles was broken.
The syntax highlighter only supports [source,js].
Also adds a check to the rest test generator that runs during
the build that'll fail the build if it sees `[source,json]`.
* Centralised plugin docs in docs/plugins/
* Moved integrations into same docs
* Moved community clients into the clients section of the docs
* Removed docs/community
Closes#11734Closes#11724Closes#11636Closes#11635Closes#11632Closes#11630Closes#12046Closes#12438Closes#12579