[#715] Forward custom headers for cdx queries

[krakan]

Description

Find custom http headers in the incoming request and forward them to the cdx-request. A custom header in this context is one prefixed with HTML_X_.

Motivation and Context

The difference between the block and exclude actions in the ACL is that the former should allow access to the index but not the data whereas the latter should block both index and data access.

See issue [#715] which is about allow_ignore_embargo not allowing access to the index when specified with a specific user. On investigation the issue also affected other use cases. The change set includes new tests for theses cases.

Types of changes

• Replay fix (fixes a replay specific issue)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added or updated tests to cover my changes.
• All new and existing tests passed.

[tw4l]

Looks good, thank you!