Allow app to set or modify workspace description

[amstilp]

• Add a "description" field to Workspace.
• Modify Workspace.anvil_import to get the description for the workspace.
• Add an AnVILAPIClient method to set workspace attributes.
• Add a WorkspaceUpdate method to modify the description. Make sure this can only update the description. This method will need to make an API call.
• Add a check for workspace description in Workspace.anvil_audit?

[amstilp]

Note that descriptions are stored in Markdown!

See possible packages to use:

• https://github.com/agusmakmun/django-markdown-editor
• https://github.com/neutronX/django-markdownx

[amstilp]

This is unlikely to happen, since in some cases we are asking investigators to update the description in AnVIL. If we do eventually decide to implement it:

• https://djangopackages.org/search/?q=markdown
• https://djangopackages.org/packages/p/django-markdownx/
• https://djangopackages.org/packages/p/draceditor/