feat: adds various OCI metrics

[ppapapetrou76]

Checklist:

• Either (a) I've created an enhancement proposal and discussed it with the community, (b) this is a bug fix, or (c) this does not need to be in the release notes.
• The title of the PR states what changed and the related issues number (used for the release note).
• The title of the PR conforms to the Title of the PR
• I've included "Closes [ISSUE #]" or "Fixes [ISSUE #]" in the description to automatically close the associated issue.
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closes #25378

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[blakepettersson]

LGTM, thanks!

[codecov]

Codecov Report

❌ Patch coverage is 95.86207% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 62.57%. Comparing base (7cdc0f9) to head (9ff85eb).

Files with missing lines	Patch %	Lines
reposerver/repository/repository.go	76.92%	3 Missing ⚠️
util/oci/client.go	76.92%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #25493      +/-   ##
==========================================
+ Coverage   62.45%   62.57%   +0.11%     
==========================================
  Files         351      352       +1     
  Lines       49490    49622     +132     
==========================================
+ Hits        30910    31049     +139     
+ Misses      15621    15616       -5     
+ Partials     2959     2957       -2     

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[blakepettersson]

QQ: Do we need to first store this and then defer the execution of the function? like

Suggested change

	defer c.OnTestRepo(c.repoURL)
	f := c.OnTestRepo(c.repoURL)
	defer f()

OnExtract, OnResolveRevision, OnDigestMetadata, OnGetTags, OnTestRepo seem to all return functions.

[ppapapetrou76]

correct :) addressed

[blakepettersson]

There's one remaining issue - in https://github.com/argoproj/argo-cd/pull/25493/files#diff-6234b055bc4370846988146ad1e76d381f6004c001407b881d1450f6fba2748eR55-R61 when processMetricFunc gets called startTime gets initiated.

In order to correctly calculate the span (ObserveOCIRequestDuration) between the start of the method and the very end of the method, we need to first get the initial function (e.g c.OnTestRepo(c.repoURL)). The actual execution of the returned function needs to happen at the very end of the method call with a defer