[SCB-616] Make access log mechanism extensible

[yhs0092]

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See details in SCB-616.
The access log pattern parse mechanism is refactored, and now the creators of AccessLogItem is loaded by SPIServiceUtils.

[coveralls]

Coverage decreased (-0.08%) to 87.418% when pulling 800c7cb on yhs0092:support_access_log_extension_dev into 517a9ff on apache:master.