Sanitize Central config request URI and headers in logs

[russcam]

This commit sanitizes the request URI and headers of
request to fetch central configuration, to redact username/password info
and sensitive headers.

• Move sanitization methods to separate Santization helper class.
• Add test to assert central config sensitive request details are redacted.
• Use Consts.Redacted wherever "[REDACTED]" is needed.

Fixes #1376

[apmmachine]

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• Start Time: 2021-08-25T00:39:09.537+0000

• Duration: 56 min 33 sec

• Commit: 646d368

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Total	19795

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[gregkalapos]

Changes LGTM.

Somewhat related: do we want to maybe change the log level of the log here. We print this as a warning (or even error?) by default and people already asked about it multiple times. When central config is not enabled in Kibana, this is expected and normal behaviour - so at least in that case I think an info log would be enough.

[russcam]

Info log level sounds good. It can probably do with some further refactoring to trim the log down to the essential information, and to detect, if possible, if central config is not enabled and log/not log appropriately.

[russcam]

I've updated use the log level defined on the FailedToFetchConfigException thrown, for logging the exception. This is Debug for 403 and 404 responses and Error for everything else. I think this can be refactored in future, to simplify the flow further.