Add support for manipulating tasks: add/remove tags, custom fields

[m-roberts]

It seems that changing the tags of tasks is not supported with the client.

Missing from Task.update:

pyclickup/pyclickup/models/__init__.py

Lines 311 to 320 in f58a5c1

	def update(
	self,
	name: str = None, # string
	content: str = None, # string
	add_assignees: ListType[Union[int, User]] = None,
	remove_assignees: ListType[Union[int, User]] = None,
	status: str = None, # string
	priority: int = None, # integer
	due_date: Union[int, datetime] = None, # integer posix time, or python datetime
	) -> Union[list, dict, Response]:

API reference:
https://clickup.com/api/clickupreference/operation/AddTagToTask/
https://clickup.com/api/clickupreference/operation/RemoveTagFromTask/

The same is true for custom fields:
https://clickup.com/api/clickupreference/operation/SetCustomFieldValue/