Datatype checking for array dtype

[rettigl]

Currently, the data type of numpy arrays is not being checked against the NX datatype, i.e. e.g. numeric arrays are treated as valid entries for NX_CHAR fields, or string arrays as valid entries for NX_NUMBER. Instead, the dtype of an array should be checked against the possible primitive datatypes.
Relevant code:

pynxtools/src/pynxtools/dataconverter/helpers.py

Line 611 in d3b15e2

"NX_CHAR": (str, np.ndarray, *np_char),

Steps to reproduce:
Follow the conversion Notebook here: https://nomad-lab.eu/prod/v1/gui/user/uploads/upload/id/iM3-bEttS060E2-GIqaSBA
The @vector attributes of the transformation classes are defined as NX_CHAR in NXmpes_arpes (which itself is a mistake, to be fixed), yet are passed as numeric arrays to the converter, which accepts them without complaint, and writes numeric arrays to the attribute.

[RubelMozumder]

@rettigl I tried the *_specsscan_conversion_to_NeXus.ipynb with the current modification available here https://github.com/FAIRmat-NFDI/pynxtools/pull/554/files. With that modification I see the warning message from the mentioned notebook as follows:

Using mpes reader to convert the given files:  
• NXmpes_arpes_config.json
• Scan1496.yaml
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/INSTRUMENT[instrument]/ELECTRONANALYSER[electronanalyser]/TRANSFORMATIONS[transformations]/analyzer_rotation/@vector should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/INSTRUMENT[instrument]/ELECTRONANALYSER[electronanalyser]/TRANSFORMATIONS[transformations]/analyzer_elevation/@vector should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/INSTRUMENT[instrument]/ELECTRONANALYSER[electronanalyser]/TRANSFORMATIONS[transformations]/analyzer_dispersion/@vector should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/SAMPLE[sample]/TRANSFORMATIONS[transformations]/sample_polar/@vector should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/SAMPLE[sample]/TRANSFORMATIONS[transformations]/offset_polar/@vector should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/SAMPLE[sample]/TRANSFORMATIONS[transformations]/sample_tilt/@vector should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/SAMPLE[sample]/TRANSFORMATIONS[transformations]/offset_tilt/@vector should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/SAMPLE[sample]/TRANSFORMATIONS[transformations]/sample_azimuth/@vector should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/SAMPLE[sample]/TRANSFORMATIONS[transformations]/offset_azimuth/@vector should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/data/@energy_indices should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/data/@angular0_indices should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/data/@angular1_indices should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: Field [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/entry_identifier written without documentation.
WARNING: The value at [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/data/@axes should be one of: (<class 'str'>, <class 'numpy.str_'>, <class 'numpy.bytes_'>), as defined in the NXDL as NX_CHAR.
WARNING: Field [/ENTRY](https://file+.vscode-resource.vscode-cdn.net/ENTRY)[entry]/data/@axes written without documentation.
The output file generated: Scan1496.nxs.

Here I see that warning massage from vector attribute. You may also see that errors from *_indices which are defined as NX_CHAR in app def.