Illumio

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* remove UserObject in favour of the more generic ModifiableObject as workloads and other objects can be created/modified by non-user entities (e.g. agents)

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* add missing fields needed to decode workload objects; implement get_workload PCE function
* remove custom fields for workload open_service_ports objects in favour of new class
* change Network class to IllumioObject subtype
* add VisibilityLevel enum

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* fix policy provisioning and add PolicyVersion object
* flesh out IPList class and add get_ip_list PCE function
* move common external_data_set and external_data_reference params into IllumioObject base class
* move modification params to UserObject
* add missing fields for ServiceBinding and PortOverride classes
* add create_service_binding function and dependent objects
* fix PCE functions to send objects rather than JSON strings
* provide more detailed error messages in case of API exceptions
* remove name requirement for virtual service init; change apply_to default to None
* fix broken build function and add error case
* add policy provision API call and dependent objects
* add LabelSet object type
* move enums to constants util module and improve validation logic

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* create more descriptive modules and move submodules from policyobjects
* change core object structure to use IllumioObject base class
* move JsonObject class to jsonutils
* standardize formatting for complex type decoding
* use IllumioEncoder rather than directly calling to_json

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* add async traffic flow function and builder function for traffic queries
* flesh out traffic analysis flow objects and add decode test
* flesh out workload object definition and subclasses
* add containercluster and vulnerabilityreport module stubs
* define extendable base enum class for package-wide use
* add Network and Vulnerability stubs for workloads
* add params to Service to accommodate Workload open_service_ports object definition
* add delete_type param to base PolicyObject
* add _validate function called from post_init in base JsonObject class
* add virtualserver stub module
* shift date validation to the API so we don't have to worry about ISO format conversion (fromisoformat isn't introduced until 3.9) or timezones
* simplify creation of query objects
* add validation for start and end dates
* add query_name field for async queries
* add traffic analysis query structure dataclasses
* add workload and iplist module stubs
* use UserObject base class and simplify init logic for simple reference cases
* combine service objects into single module and simplify class structures
* add User object and separate UserObject base class for user-created policy objects
* use socket lib function rather than custom protocol enum for conversion to int
* move JsonObject base class into policyobject module
* add pytest cache to gitignore

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* improve virtual service tests
* overhaul policy object structures and improve json encoding/decoding
* remove api module