clp-core: Add custom headers support for NetworkReader

[anlowee]

Description

Modified constructors of NetworkReader, DownloaderThread and CurlDownloadHandler to support custom headers passed by users.

Validation performed

Added the Authorization header with a Bearer token to fetch a file from remote, validating the file's size.

Summary by CodeRabbit

• New Features

  • Enhanced CurlDownloadHandler and NetworkReader constructors to accept custom HTTP headers, allowing for more flexible HTTP requests.
  • Custom headers can now be specified during the instantiation of both CurlDownloadHandler and NetworkReader.

• Tests

  • Added a new test case for NetworkReader to validate the handling of custom HTTP headers, ensuring expected headers are included and illegal ones are excluded.

• Bug Fixes

  • No specific bug fixes were noted in this release.

• Documentation

  • Updated constructor signatures to reflect the addition of the custom headers parameter.