Add support for ingressClassName in flyte-core

[davidmirror-ops]

Why are the changes needed?

As the kubernetes.io/ingressClass annotation is deprecated since K8s 1.18, this PR adds support for the new mechanism (ingressClassName) to flyte-core.

This is useful in environments where there are multiple Ingress controllers running or, when cert-manager's ingress-shim is configured to generate SSL certificates for Ingress resources, using the ingressClassName as selector.

What changes were proposed in this pull request?

How was this patch tested?

Setup process

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Check all the applicable boxes

• I updated the documentation accordingly.
• All new and existing tests passed.
• All commits are signed-off.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (91d24a9) 58.98% compared to head (e4f46d0) 58.98%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4551   +/-   ##
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  Coverage   58.98%   58.98%           
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  Files         621      621           
  Lines       52483    52483           
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+ Hits        30957    30958    +1     
+ Misses      19059    19058    -1     
  Partials     2467     2467           

Flag	Coverage Δ
unittests	58.98% <100.00%> (+<0.01%)	⬆️

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[eapolinario]

Small typo in the description: it should say k8s 1.18 not 1.28, right?

On a related note, how can we determine what's the minimal supported version of k8s?

[davidmirror-ops]

Small typo in the description: it should say k8s 1.18 not 1.28, right?

On a related note, how can we determine what's the minimal supported version of k8s?

Typo fixed.

Regarding upstream K8s version skew policy, it's basically n-2. For older versions, it's only time-limited patch support.