feat: Respect original parameter overrides with git write-back

[ks-yim]

Modification:

Make image-updater respect the original parameter overrides written in .argocd-source-<appName>.yaml.

Motivation:

Currently, the original overridden parameters stored in .argocd-source-<appName>.yaml
are not respected when image-updater writes back its change to git.

Imagine that a user has originally defined .argocd-source-<appName>.yaml like below

helm:
  parameters:
  - name: some.prop
    value: some-value
    forcestring: true

...and image-updater wants to write back the additional overrides below

• foo.image.repository: foo
• foo.image.tag: 2.0.0

The user may want the edited file to be like...

helm:
  parameters:
  - name: some.prop
    value: some-value
    focestring: true
  - name: foo.image.repository
    value: foo
    forcestring: true
  - name: foo.image.tag
    value: 2.0.0
    forcestring: true

... but what's actually committed to git is the following and it deletes the original user-defined parameter overrides.

helm:
  parameters:
  - name: foo.image.repository
    value: foo
    forcestring: true
  - name: foo.image.tag
    value: 2.0.0
    forcestring: true

And this image-updater behavior is a suspected cause of #562 and the likes
as image-updater ignores the tags for an image that it failed to fetch when
there are multiple updatable images defined in an Application and generate
the parameter overrides without the ignored image.
If only a part of image tags were successfully fetched from the image registry
due to unstable network, image-updater may write a broken parameter override
file to git.

[codecov-commenter]

Codecov Report

Merging #573 (4a9f69d) into master (5366cc1) will decrease coverage by 0.24%.
The diff coverage is 41.02%.

@@            Coverage Diff             @@
##           master     #573      +/-   ##
==========================================
- Coverage   65.86%   65.63%   -0.24%     
==========================================
  Files          22       22              
  Lines        2045     2069      +24     
==========================================
+ Hits         1347     1358      +11     
- Misses        569      577       +8     
- Partials      129      134       +5     

Impacted Files	Coverage Δ
pkg/argocd/update.go	66.05% <35.71%> (-3.75%)	⬇️
pkg/argocd/git.go	66.82% <54.54%> (+1.98%)	⬆️

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[jannfis]

Nice one, thank you!

The linter complained, and it turns out your code shadows err in one place. Please fix it, otherwise LGTM :)

[jannfis]

Suggested change

	err := yaml.Unmarshal(originalData, &params)
	err = yaml.Unmarshal(originalData, &params)

[jannfis]

Oh, and please make sure the DCO passes by signing off your commits

[ks-yim]

@jannfis
Thanks for taking your time to review this!

The issue described in the PR description has actually caused a disruption to our production(insignificant, though) workload so it would be very nice if I can ship this into the next release.

Resolved the variable shadowing issue and signed-off all my commits included in the PR.
I tried to make it pass Spell checking and Run codegen by merging the latest master but had no luck. 😅

[jannfis]

Thanks for looking into it, @ks-yim!

I have just merged #590 , so if you rebase your PR, the codegen step should pass.

I'm aiming to release v0.13.0 after #578 has been merged, however, it needs some attention from the submitter.

[jannfis]

LGTM. Going to merge it without rebase required, because the codegen error is negligible.