[SYSTEMDS-3330] Documentation of builtin functions (main)

This commit adds new automatic generation of separated doc files for all
builtin functions, and automatic generation of tests for builtin functions.
All based on the original documentation in individual builtin scripts.

This change will simplify the development of builtin functions and help new
users across both the Python api and internal DML testing.

An example of documented code is:

.. code-block:: python

  >>> import numpy as np
  >>> from systemds.context import SystemDSContext
  >>> from systemds.operator.algorithm import dist
  >>>
  >>> with SystemDSContext() as sds:
  ...     X = sds.from_numpy(np.array([[0], [3], [4]]))
  ...     out = dist(X).compute()
  ...     print(out)
  [[0. 3. 4.]
   [3. 0. 1.]
   [4. 1. 0.]]

Closes #2292