Add docs for plugin development

[ajatprabha]

No description provided.

[codecov]

Codecov Report

Merging #4276 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4276      +/-   ##
==========================================
- Coverage   46.59%   46.56%   -0.03%     
==========================================
  Files         200      200              
  Lines        9373     9365       -8     
  Branches      105      105              
==========================================
- Hits         4367     4361       -6     
+ Misses       4738     4735       -3     
- Partials      268      269       +1

Impacted Files	Coverage Δ
...p/backend/integration/metric/common/aggregation.go	89.09% <0%> (-1.82%)	⬇️
...c/app/backend/integration/metric/sidecar/client.go	72% <0%> (-1.69%)	⬇️
src/app/backend/sync/secret.go	73.26% <0%> (+2.97%)	⬆️

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[shu-mutou]

Could you add link for this into https://github.com/kubernetes/dashboard/blob/master/docs/README.md ?

[shu-mutou]

Related to #4008.

[ajatprabha]

@shu-mutou Should this be mentioned under a separate category or under Developer Guide?

[shu-mutou]

@ajatprabha I think this should be described for third party that includes both of user and developer.

[maciaszczykm]

/lgtm
/approve

It's good as a first step. I'd like to have more infor about how to write plugins, what we can use, even some samples with screenshots showing the active plugin in the UI.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ajatprabha, maciaszczykm

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[xm2]

kubernetes configmap has size limitation, (<=1MB), so the compiled plugin javascript file should not exceed 1MB. That is the limitation of this plugin solution, right?

[ajatprabha]

Yes, you're right. We can look into other ways to obtain the compiled plugin file instead of just configmap. We wanted to keep dashboard stateless and using configmaps was the easiest way to tackle this for now.