Update dependency kubernetes to v21

This MR contains the following updates:

Package	Type	Update	Change
kubernetes	ironbank-pypi	major	20.13.0 -> 21.7.0

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Release Notes

kubernetes-client/python

v21.7.0

Compare Source

Kubernetes API Version: v1.21.7

Bug or Regression

• Fixed #​741, an issue which prevented Kubernetes cluster api-tokens from exec-plugin auth providers from being refreshed after expiry. (#​250, @​emenendez)
• Use select.poll() for exec on linux/darwin to improve scalability of WSClient (#​268, @​jsun-splunk)

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