Docs: Update Dex config, change misleading error message.

[EladLeev]

Signed-off-by: Elad Leev eladleev@gmail.com

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Description:
Hi :)
Creating this PR to update some of the Dex documentation, and to change a misleading error message on ReplaceStringSecret.

Dex changes:

• The part-of label is missing from the Secret example, so it won't be associate it with Argo.
• Explicitly specify that we are using the OIDC account details, and not the service-account details.
• Mention that setting the URL is used to enable Dex.

Log changes:

• Mention the annotation as part of the log. Without it, it's a bit misleading, as it seems that the secret was loaded properly, but the key is missing from it, wrong, or need to be escaped.

Thanks! 💪

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.01 ⚠️

Comparison is base (918e19e) 49.73% compared to head (f8a28a9) 49.72%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11208      +/-   ##
==========================================
- Coverage   49.73%   49.72%   -0.01%     
==========================================
  Files         261      261              
  Lines       44705    44705              
==========================================
- Hits        22234    22231       -3     
- Misses      20284    20286       +2     
- Partials     2187     2188       +1     

Impacted Files	Coverage Δ
util/settings/settings.go	51.09% <100.00%> (ø)

... and 1 file with indirect coverage changes

☔ View full report in Codecov by Sentry.
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[iam-veeramalla]

Hi @EladLeev Can you please explain what was the impact of not having this before ?

[EladLeev]

Thank you for taking a look at this PR @iam-veeramalla!

Without this label, ArgoCD won't consider this secret as part of ArgoCD, and won't read it at all.
Correct me if I'm wrong, but using this label, argo select and parse related secrets.
Without it, Argo will just use the default secret (argocd-secret).

This also relates to the rest of the changes that I've made - when this label is absent, and you are referring to a different secret (using $<k8s_secret_name>:<key>) the error that you'll get is -

config referenced '%s', but the key does not exist in secret

Which is a bit misleading as you are not really reading that secret and not finding the key.

side note: I think that it's better to add validations and a custom errors when referring to a secret that is not labelled, but I didn't want to make too many changes to settings.go on my first contribution 😅

[iam-veeramalla]

Are you adding this manually today in your setup ?