* Reduce linting severity for users of out-of-date kubernetes

Fixes #8596
Signed-off-by: Joe Julian <me@joejulian.name>

* add more verbose deprecation info
Signed-off-by: Joe Julian <me@joejulian.name>

* use new upstream deprecations
Signed-off-by: Joe Julian <me@joejulian.name>

* do not error for custom resources
Signed-off-by: Joe Julian <me@joejulian.name>

* Define deprecation version in lint rules by LDFLAG
Signed-off-by: Joe Julian <me@joejulian.name>

* make comment clearer
Signed-off-by: Joe Julian <me@joejulian.name>

* Extend the k8s version discovery and constants to chartutil
Signed-off-by: Joe Julian <me@joejulian.name>

* remove awk dependency
Signed-off-by: Joe Julian <me@joejulian.name>

* align k8s version constant names between capabilities.go and deprecations.go
Signed-off-by: Joe Julian <me@joejulian.name>

* show the error if the unexpected happens
Signed-off-by: Joe Julian <me@joejulian.name>

* bump k8sVersionMinor and golden chart templates for k8s 1.20
Signed-off-by: Joe Julian <me@joejulian.name>

* bump for tests to match 1.20.1
Signed-off-by: Joe Julian <me@joejulian.name>