feat: add support for Kubernetes 1.21.0-beta.0

[mboersma]

Reason for Change:

See https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG/CHANGELOG-1.21.md#changelog-since-v1210-alpha3

Issue Fixed:

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

Requirements:

• Kubernetes artifacts built and pushed by Azure Pipelines
• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mboersma

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Needs approval from an approver in each of these files:

• OWNERS [mboersma]

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[codecov]

Codecov Report

Merging #4300 (e36a4cd) into master (edeee21) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4300   +/-   ##
=======================================
  Coverage   72.03%   72.03%           
=======================================
  Files         141      141           
  Lines       21633    21633           
=======================================
  Hits        15584    15584           
  Misses       5099     5099           
  Partials      950      950           

Impacted Files	Coverage Δ
pkg/api/common/versions.go	96.37% <ø> (ø)

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