Add support to CTA for multiple tape label formats

Problem to solve

CTA needs to add support for reading OSM/dCache and Enstore tape formats, as agreed at the EOS Workshop 2022 BoF.

The dCache devs have a working proof-of-concept implementation, see details in https://gitlab.cern.ch/cta/CTA/-/merge_requests/187

To properly integrate this feature into CTA, we should refactor the code in CTA/tapeserver/castor/tape/tapeserver/file/File.cpp.

Stakeholders

• dCache developers
• Fermilab/Enstore replacement developers

Proposal

First, some refactoring:

• Refactor CTA/tapeserver/castor/tape/tapeserver/file/File.cpp to separate the classes in that file into separate .cpp files:
  • LabelSession
  • ReadSession
  • HeaderChecker
  • ReadFile
  • WriteSession
  • WriteFile
• Add helper methods to ReadSession and ReadFile classes to abstract out the specific details of how to read the tape file. See https://gitlab.cern.ch/cta/CTA/-/merge_requests/187 and in particular https://gitlab.cern.ch/cta/CTA/-/merge_requests/187#note_5597846 for an overview of which helper functions are needed.
• Change the helper methods in ReadSession and ReadFile into pure virtual functions. Create subclasses (example names: CtaReadSession and CtaReadFile) and move the CTA helper method implementations into those classes.
• Instantiate on the appropriate subclass of ReadFile when we call openReadFile (currently returns a smart pointer to a ReadFile object, it can return CtaReadFile instead). Same for ReadSession and openReadSession.

After this refactoring is done, we should add this to a release and deploy, to ensure there are no regressions.

Then we can add in the dCache OSM label format implementation:

• Add empty subclasses OsmReadSession and OsmReadFile
• Modify openReadFile and openReadSession to check the label format. If it is OSM format, return the OSM classes. Otherwise, by default return CTA label format classes.
• dCache developers can add their implementation.

The last 3 points above can be repeated for the Enstore format.