Fix Kubernetes auth broken for 1.24+ kubectl versions

[rabbitfang]

Description

client.authentication.k8s.io/v1alpha1.ExecCredential was removed in Kubernetes 1.24. v1 is GA, but is not supported before 1.22. In the meantime, we can use v1beta1, which should be supported for a while. See aws/aws-cli#6920 for more info on this bug.

Safety checklist

• This change is backwards compatible and safe to apply by existing users
• This change will NOT lead to data loss
• This change will NOT lead to downtime who already has an env/service setup

How has this change been tested, beside unit tests?

Verified that this works with kubectl v1.24 and awscli v2.6.4. I need someone to verify that it works on older kubectl and awscli versions.

[codecov]

Codecov Report

Merging #879 (93473bf) into main (12602fa) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 93473bf differs from pull request most recent head 3a12ecc. Consider uploading reports for the commit 3a12ecc to get more accurate results

@@           Coverage Diff           @@
##             main     #879   +/-   ##
=======================================
  Coverage   72.90%   72.91%           
=======================================
  Files         122      122           
  Lines        8279     8281    +2     
=======================================
+ Hits         6036     6038    +2     
  Misses       2243     2243           

Flag	Coverage Δ
unittests	72.91% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
opta/core/aws.py	56.25% <100.00%> (+0.34%)	⬆️

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