feat: Allow users to template and render Application's resources fully locally

[Sergey-Kizimov]

This PR is an attempt to make the argocd app manifests command run completely local, a pre-rendered file with app objects is required for correct operation.
I hope, this PR should close #11129

example command run:
argocd app manifests my-app-name --local-app-manifest /repo/my-app/application/my-app.yaml --local /repo/my-app/manifests --local-repo-root /repo/my-app

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[codecov]

Codecov Report

❌ Patch coverage is 0.95238% with 104 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.83%. Comparing base (15254af) to head (2dfff9a).
⚠️ Report is 3141 commits behind head on master.

Files with missing lines	Patch %	Lines
cmd/argocd/commands/app.go	0.00%	68 Missing ⚠️
cmd/util/app.go	2.77%	35 Missing ⚠️
cmd/argocd/commands/admin/app.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #14365      +/-   ##
==========================================
- Coverage   49.90%   49.83%   -0.07%     
==========================================
  Files         262      262              
  Lines       45129    45192      +63     
==========================================
  Hits        22523    22523              
- Misses      20391    20454      +63     
  Partials     2215     2215              

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[Sergey-Kizimov]

Now we can filter by application name from 1 file with multiple applications

[savar]

Is there any plan to merge this?

[pkalemba]

Can we merge this?

[andrii-korotkov-verkada]

Why do we need a separate filterByAppName?

[tewe]

I think in case the file given as --local-app-manifest contains multiple YAML documents.

[nerdware-timmmi]

Again the question is: Is there any plan to merge this?

I would be very happy about the addition of this feature.

[agaudreault]

Since this is a command that should run 100% locally, it is a very good candidate to use with the new cli-plugin feature
https://argo-cd.readthedocs.io/en/latest/user-guide/plugins/. It will avoid the current command from being cluttered with arguments that are or may be necessary for local generation in the future.

Many parameters in the config map can affect the application generation. The constraint to not have access to these config will need to be resolved by either providing them as arguments, or as a configFile.

I will close this PR, but let the issue open.

[pkalemba]

@agaudreault Correct me if I'm wrong, but my understanding was that we intended to use ArgoCD's internal flow for rendering manifests. If we use a plugin, we would need to replicate that flow, which essentially means re-implementing core ArgoCD functionality. Is that correct?

[agaudreault]

@pkalemba you can write a go application that will reuse the argo libraries