Add ability to provide a custom form for Workspaces

[amstilp]

• Add a new Workspace adapter attribute, workspace_form_class, that users can set to provide a custom form for Workspaces
• Rename WorkspaceCreateForm to WorkspaceForm
• Remove the WorkspaceUpdateForm and instead subclass the Workspace form in WorkspaceUpdate
• Use the adapter to get the form class for WorkspaceCreate and WorkspaceUpdate

[codecov[bot]]

Codecov Report

Merging #394 (622fb25) into main (993e09c) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #394   +/-   ##
=======================================
  Coverage   99.42%   99.42%           
=======================================
  Files         118      118           
  Lines       21782    21872   +90     
=======================================
+ Hits        21657    21747   +90     
  Misses        125      125           

Files	Coverage Δ
anvil_consortium_manager/__init__.py	100.00% <100.00%> (ø)
anvil_consortium_manager/adapters/default.py	100.00% <100.00%> (ø)
anvil_consortium_manager/adapters/workspace.py	100.00% <100.00%> (ø)
anvil_consortium_manager/forms.py	100.00% <100.00%> (ø)
anvil_consortium_manager/models.py	100.00% <ø> (ø)
anvil_consortium_manager/tests/test_adapters.py	100.00% <100.00%> (ø)
...nvil_consortium_manager/tests/test_app/adapters.py	100.00% <100.00%> (ø)
anvil_consortium_manager/tests/test_app/forms.py	100.00% <100.00%> (ø)
anvil_consortium_manager/tests/test_forms.py	100.00% <100.00%> (ø)
anvil_consortium_manager/tests/test_views.py	99.92% <100.00%> (+<0.01%)	:arrow_up:
... and 1 more

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