Method to update only selected custom fields

[TytoCapensis]

Added api.update_case_customfields(). This method allows to update only selected custom fields (instead of update them all at once), which can be useful for:

• having automations on the filling of a custom field (such as a webhook) ;
• preventing conflicts linked to race conditions when several automations are running on custom fields (For more details, see https://github.com/TheHive-Project/TheHive/issues/1839 )

(Please note that this PR adds a new file (utils.py), and that despite I tested the code with several dummy values, this should still be beta-tested before release)

[wizedkyle]

Are there any plans to merge this PR as we have a use case for updating single customFields and this would make life a lot easier?

[Kamforka]

@wizedkyle is this feature still relevant to you or you moved to v5 in the meantime?

[Kamforka]

We are closing this PR as it targets the 1.x version of thehive4py, which is no longer supported.