Type conversions for Python Series constructor

[franzpoeschel]

Closes #1723

• Can now pass Path for filepath parameter of constructor
• Can now pass JSON dicts for options parameter of constructor (will internally call json.dumps()

TODO

• The constructor can at the moment not automatically distinguish if the parameter is an MPI communicator or a JSON object since both overloads accept py::object, making explicit options={} necessary. Maybe find a way to fix this somehow..?
• Document new internal CMake option
• Testing, examples
• Use -DopenPMD_USE_FILESYSTEM_HEADER in some CI run
• Enable <filesystem> header for prebuilt Wheels?