Add environment variable to disable summarization cron tasks

[sainak]

• Add environment variables to disable specific summarization tasks, they should be allowed to un by default
• Update docs

https://github.com/coronasafe/care/blob/ef73d9368fc8df775688c497acbd4e17fd9ba1a2/care/facility/tasks/__init__.py#L23-L47

the variable names should be in the pattern TASK_SUMMARIZE_*

[amjithtitus09]

Hey @sainak can you assign me this issue?

[amjithtitus09]

@sainak Could you please share the link of the doc to be updated?

[sainak]

@amjithtitus09 there is no doc for environment variables, but you can create a new file under /docs/django-configuration and add the new variables, with a brief description and examples under the environment variables section