Deprecate Probability field on Opportunity (#6207)

Closes #5735.
The field probability on opportunity will -
- stop being created for new workspaces (after this PR is merged)
- have "isCustom" value set to true and be displayed as such in the
settings (after this PR is merged + sync-metadata is run on workspace)
- still show in the views (all the time)

This field is deprecated as a standard field but not replaced by another
one, so we are not adding the `(deprecated)` suffix in the label.

packages/twenty-front/src/testing/mock-data/view-fields.ts

@@ -142,14 +142,6 @@ export const mockedViewFieldsData = [
     isVisible: true,
     size: 180,
   },
-  {
-    id: 'e5a731bb-82b9-4abe-ad22-1ddea94722f9',
-    fieldMetadataId: 'probability',
-    viewId: mockedViewsData[2].id,
-    position: 1,
-    isVisible: true,
-    size: 150,
-  },
   {
     id: '3159acd8-463f-458d-bf9a-af8ac6f57dc0',
     fieldMetadataId: 'closeDate',