feat: Add env vars config for argo-server and workflow-controller

[prichrd]

This is a proposal for #5914. It uses https://github.com/spf13/viper to parse environment variables from the flag names.

I tested this like this:

[prichrd]

Please let me know if this needs more tests.

[alexec]

Looks good, so simple. Can we add some docs about this?

[codecov]

Codecov Report

Merging #6767 (bea64cc) into master (7684ef4) will increase coverage by 0.05%.
The diff coverage is 81.57%.

❗ Current head bea64cc differs from pull request most recent head 38bf4aa. Consider uploading reports for the commit 38bf4aa to get more accurate results

@@            Coverage Diff             @@
##           master    #6767      +/-   ##
==========================================
+ Coverage   48.64%   48.70%   +0.05%     
==========================================
  Files         264      265       +1     
  Lines       19076    19108      +32     
==========================================
+ Hits         9279     9306      +27     
- Misses       8752     8757       +5     
  Partials     1045     1045              

Impacted Files	Coverage Δ
cmd/argo/commands/server.go	30.14% <50.00%> (-0.63%)	⬇️
workflow/controller/dag.go	76.38% <77.77%> (+0.99%)	⬆️
util/expand/expand.go	100.00% <100.00%> (ø)
workflow/controller/workflowpod.go	74.18% <100.00%> (+0.10%)	⬆️
workflow/validate/validate.go	76.70% <100.00%> (+0.73%)	⬆️
server/workflow/workflow_server.go	44.41% <0.00%> (-2.40%)	⬇️
workflow/controller/operator.go	71.06% <0.00%> (-0.15%)	⬇️
cmd/argo/commands/get.go	58.89% <0.00%> (+0.58%)	⬆️
... and 3 more

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[prichrd]

@alexec I'll update the following doc this evening:

• https://github.com/argoproj/argo-workflows/blob/master/docs/argo-server.md

What doc should I update for the workflow-controller?

[alexec]

I think the right places is probably:

https://github.com/argoproj/argo-workflows/blob/master/docs/environment-variables.md

[alexec]

I was wrong about where to add those flags. It fails make codegen. It also means that we need the keep that list up-to-date - which we will fail to do.

Instead, can I ask you to just add a bit like this:

Parameters can be specified as environment variables:

  workflow-controller --managed-namespace=argo

Can be expressed as:

  env MANAGED_NAMESPACE=argo workflow-controller

[alexec]

Please dismiss review when done.

[prichrd]

That makes total sense. I will update the docs/environment-variables.md doc to reflect that suggestion.

[alexec]

Is it possible to have ARGO_ as prefix?

[prichrd]

It shouldn't be an issue, it is fairly simple to do with Viper's SetEnvPrefix, I'll fix that.

[prichrd]

@alexec, done!

[alexec]

🚀