docs: full copy-edit of environment-variables.md

[agilgur5]

Motivation

environment-variables.md had some inconsistencies and mistakes in it.

• I've linked to it a few times and have added relative links from other places in the docs, so would like to make sure the page is accurate etc

Modifications

Accuracy fixes

• move Server env vars and examples into the Server section
  • instead of being in the Controller block
  • GRPC_MESSAGE_SIZE was used in the example yet wasn't in the Server's env var list
    • it was incorrectly in the Controller list, confirmed it was only used in Server code
    • also add its previously missing default into the table
  • also comment out ellipses in code block so that the block is all valid code

Consistency

• consistently use 1 sentence per line

• consistently use "Server and Controller" instead of argo-server and workflow-controller (or the lowercase variants)

  • consistent with the rest of this page and the rest of the docs
  • those names are primarily referenced in the manifests

• consistently use the sentence "You can set environment variables [...] like the following"

  • there were a few variations on this before
  • consistently use "Deployment's container spec"
    • similarly a few variations before

Misc

• be more direct with the first line description of the document, per k8s style guide

• use !!! Warning block instead of a unicode character

  • this is more consistent with the rest of the docs and a more clear warning

• link to the workflow-controller-configmap when it is mentioned

  • keep references to it consistent across the docs; always use workflow-controller-configmap

Verification

make docs and make codegen pass