Add support to add a logfilter

[rf232]

What this PR does / why we need it:

To implement log sanitization according to KEP-1753 we need to be able
to install a LogFilter method that can replace the arguments to logging
statements to prevent accidental leaking of secrets, certificates or
passwords.

Special notes for your reviewer:

https://github.com/kubernetes/enhancements/tree/master/keps/sig-instrumentation/1753-logs-sanitization

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

Release note:

Add support to add a logfilter to support log sanitization.

The interface of the filter defines three functions for the three kinds
of logging functions exposed by klog.

type LogFilter interface {
  Filter(args []interface{}) ([]interface{})
  FilterF(format string, args []interface{}) (string,[]interface{})
  FilterS(msg string, keysAndValues []interface{}) (string, []interface{})
}
In the case this is used for log sanitization each of these functions should inspect the arguments and if they contain sensitive data alter the arguments to make sure there is no leaking.

[serathius]

/assign

[serathius]

/assign @44past4

[serathius]

/lgtm

[serathius]

/assign @justinsb

[serathius]

/cc @dims

[dims]

/approve

will leave LGTM to someone else!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dims, rf232, serathius

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[44past4]

/lgtm

[pohly]

Why was filter added to Verbose and as parameter to all the other functions? That causes overhead and the only advantage that I see is that in the theoretic case that someone does V + SetFilter, the original filter will be used when logging through the Verbose instance. I'm not even sure whether that is desirable.