Add Secure logs level support

[imjaroiswebdev]

Add support for an extra logging level capability for PagerDuty Terraform Provider, allowing to log http request/response obscuring the API Key from Authorization header only printing last four characters of header's value utilizing the template <OBSCURED>4cha.

New test cases introduced...

$ make test TESTARGS="-v -run SecureLogger"
==> Testing go-pagerduty
=== RUN   TestSecureLoggerHandleHeadersLogsContent
--- PASS: TestSecureLoggerHandleHeadersLogsContent (0.00s)
=== RUN   TestSecureLoggerHandleBodyLogsContent_JSON
--- PASS: TestSecureLoggerHandleBodyLogsContent_JSON (0.00s)
=== RUN   TestSecureLoggerHandleBodyLogsContent_NonJSON
--- PASS: TestSecureLoggerHandleBodyLogsContent_NonJSON (0.00s)
=== RUN   TestSecureLoggerCanLog
--- PASS: TestSecureLoggerCanLog (0.00s)
=== RUN   TestSecureLoggerLogReq
--- PASS: TestSecureLoggerLogReq (0.00s)
=== RUN   TestSecureLoggerLogRes
--- PASS: TestSecureLoggerLogRes (0.00s)
PASS
ok      github.com/heimweh/go-pagerduty/pagerduty       0.527s