RFE: Adding hyperlinks with any role for work items

[KwisatzHaderach]

We need to be able to add hyperlinks with any role to test cases, which is currently not possible with pylero, only with Web UI.

>>> tc.hyperlinks[1].role
testscript1
>>> tc.add_hyperlink('https://github.com', 'testscript1')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/pmatyas/.local/lib/python3.10/site-packages/pylero/work_item.py", line 622, in add_hyperlink
    self.check_valid_field_values(role, "hyperlink-role", {})
  File "/home/pmatyas/.local/lib/python3.10/site-packages/pylero/base_polarion.py", line 995, in check_valid_field_values
    raise PyleroLibException(
pylero.exceptions.PyleroLibException: Acceptable values for hyperlink-role are:[ref_int, ref_ext]