Add canvas support

[sergey-misuk-valor]

Add possibility to create signatures from CeleryTaskModel instance.

Right now jobs created by inheriting CeleryTaskModel can be used in pretty simple scenarios. There is number of primitives in Celery that allow running tasks in sequence or in parallel:

group

The group primitive is a signature that takes a list of tasks that should be applied in parallel.

chain

The chain primitive lets us link together signatures so that one is called after the other, essentially forming a chain of callbacks.

chord

A chord is just like a group but with a callback. A chord consists of a header group and a body, where the body is a task that should execute after all of the tasks in the header are complete.

But in order to use them we need a support for signatures. A signature is a representation of a task that can be passed around. Though we can still create signatures from the raw Celery tasks, we loose connection between CeleryTaskModel and it's underlying task.

This feature allows generation of signatures from CeleryTaskModel. Those signatures contain not only information required for task execution, but also information required to update CeleryTaskModel status

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.55556% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 94.37%. Comparing base (48a3afe) to head (a8d5591).

Files with missing lines	Patch %	Lines
src/django_celery_boost/task.py	92.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop       #6      +/-   ##
===========================================
+ Coverage    94.31%   94.37%   +0.05%     
===========================================
  Files            4        5       +1     
  Lines          352      391      +39     
  Branches        39       41       +2     
===========================================
+ Hits           332      369      +37     
- Misses          14       15       +1     
- Partials         6        7       +1     

Flag	Coverage Δ
unittests	94.37% <95.55%> (+0.05%)	⬆️

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[saxix]

please add human readable summary of the feature in the PR. what is the feature that we are adding from the "business/client/utiliser" point of view