Emitting a log message containing the request fingerprint when storing a page

[starrify]

This is idea of a new feature.

Use case:
When PAGE_STORAGE_ON_ERROR_ENABLED is enabled and there're errors encountered in a job, a user may want to check the corresponding page contents after having read the log messages.
However it might sometimes be difficult to locate the very record in Scrapinghub Collections. With the request fingerprint provided in the log messages, a user may easily locate the record by querying the fingerprint value as the key.

[vshlapakov]

I'm not an active user of the addon, but the feature description sounds good and it's something that should be easy to implement, PR is welcome.