docs(helm): add required env for docker-in-docker

[cjtim]

Fixes #199
Hi, I see there's an example of docker in docker in extraContainers
but in order to use it, you need to set DOCKER_HOST in code-server too

I think it a good idea to add more since we already had dind in extraContainers

Working in my RKE cluster v1.21.10

[jsjoeio]

Thanks for adding this!

[codecov]

Codecov Report

Merging #5045 (851e976) into main (5341294) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #5045   +/-   ##
=======================================
  Coverage   71.30%   71.30%           
=======================================
  Files          30       30           
  Lines        1683     1683           
  Branches      373      373           
=======================================
  Hits         1200     1200           
  Misses        413      413           
  Partials       70       70           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5341294...851e976. Read the comment docs.