Add support for entities

[kelvin-muchiri]

Changes / Features implemented

• Add EntityList, RegistrationForm, FollowUpForm models
• Automatically create Entity when a RegistrationForm receives a submission
• Upgrade pyxform to a version that supports entities definition
• Add endpoints to fetch Entities releated data
• Replace all occurrences of xml.dom.minidom.parseString with defusedxml.minidom.parseString to avoid threats of XML attacks https://pypi.org/project/defusedxml
• Add new model GenericExport for storing export related data for EntityList datasets and any other objects in future that may need to have exports

Steps taken to verify this change does what is intended

• QA

Side effects of implementing this change

Before submitting this PR for review, please make sure you have:

• Included tests
• Updated documentation

Closes #2500

[ukanga]

Could we have used onadata.libs.utils.logger_tools.create_xform_version(xform: Xform, user: User)?

Perhaps, could we consider adding publish_md_form() similar to the publish_xls_form() and publish_xml_form() functions under onadata.libs.utils.logger_tools that have the same signature and all create the XFormVersion object of the form they publish? This will mean we update self._publish_markdown() to use the new publish_md/markdown_form() function and an XFormVersion object will always be created when publishing the form.

[kelvin-muchiri]

Could we have used onadata.libs.utils.logger_tools.create_xform_version(xform: Xform, user: User)?

@ukanga Since this is a test we should assume onadata.libs.utils.logger_tools.create_xform_version does not exist in order to avoid coupling the tests with actual implementations. Also, using TDD, we wouldn't expect onadata.libs.utils.logger_tools.create_xform_version to exist

[ukanga]

@kelvin-muchiri There are several places where the XFormVersion is directly created. So, if we apply this change only in self._publish_markdown(), the repetition can be avoided.

[ukanga]

I agree we may not need to create publish_md/markdown_form() unless we see future potential for it. The main reason to consider it is to ensure we do not repeat or forget some steps, like, in this case, the function self._publish_markdown() forgot to create this object that should always be present when publishing a form.

[kelvin-muchiri]

@ukanga I resolved this by removing the redundant _publish_markdown in TestAbstractViewSet and inheriting TestBase