Populate the Package notice_text from Scan "key files" #136

[tdruez]

This implementation is similar to the way a copyright is "inferred" using the holder data from the Scan during the "update_from_scan" process when the Dataspace "Update packages automatically from scan" feature is enabled.

If a notice_text is not available directly on the "DETECTED PACKAGE" data returned in the Scan results, the key files content is used to generated content for the notice_text.
Only the key files with "notice" (case is ignored) in their filename are included.
In case of multiple "notice" key files, their content is combined before being assigned to the Package.notice_text

[DennisClark]

@tdruez All my tests in staging were successful.