ht.random.randint size type requirement inconsistent with NumPy API

[ClaudiaComito]

Description
int type should be allowed for size argument of ht.random.randint()

>>> import numpy as np
>>> import heat as ht
# numpy
>>> a = np.random.randint(0, 50, 20)
>>> a
array([34, 30, 43, 37, 39, 15,  9, 19, 38, 19, 12, 14, 41, 32, 44,  2,  5,
        0,  6, 45])
>>> a = np.random.randint(0, 50, size=20)
>>> a
array([10,  6, 38, 19, 10, 44,  9, 40, 23, 40, 23, 46, 41, 40,  7,  3, 15,
       25, 39, 46])

#heat
>>> b = ht.random.randint(0, 50, 20)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/c.comito/HAF/heat/heat/core/random.py", line 531, in randint
    shape = tuple(int(ele) for ele in size)
TypeError: 'int' object is not iterable

>>> b = ht.random.randint(0, 50, size=20)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/c.comito/HAF/heat/heat/core/random.py", line 531, in randint
    shape = tuple(int(ele) for ele in size)
TypeError: 'int' object is not iterable

 b = ht.random.randint(0, 50, size=(20,))
>>> b
DNDarray([13, 33,  0, 41,  6, 40, 39,  5, 34, 44,  3, 39,  1, 44, 25, 14, 25, 39, 41,  8], dtype=ht.int32, device=cpu:0, split=None)
>>> 

To Reproduce
Steps to reproduce the behavior:

see examples above

Expected behavior
it should be possible to pass an int as size argument, also in accordance with the function's type hints: size: 'Optional[Union[int, Tuple[int]]]' = None

Version Info
main branch