Refactor onboarding user vars to be absent when user is fully onboarded (#6531)

In this PR:
- take feedbacks from: https://github.com/twentyhq/twenty/pull/6530 /
https://github.com/twentyhq/twenty/pull/6529 /
https://github.com/twentyhq/twenty/pull/6526 /
https://github.com/twentyhq/twenty/pull/6512
- refactor onboarding uservars to be absent when the user is fully
onboarded: isStepComplete ==> isStepIncomplete
- introduce a new workspace.activationStatus: CREATION_ONGOING

I'm retesting the whole flow:
- with/without BILLING
- sign in with/without SSO
- sign up with/without SSO
- another workspaceMembers join the team
- subscriptionCanceled
- access to billingPortal

packages/twenty-server/src/modules/opportunity/standard-objects/opportunity.workspace-entity.ts

@@ -13,6 +13,7 @@ import {
 import { BaseWorkspaceEntity } from 'src/engine/twenty-orm/base.workspace-entity';
 import { WorkspaceEntity } from 'src/engine/twenty-orm/decorators/workspace-entity.decorator';
 import { WorkspaceField } from 'src/engine/twenty-orm/decorators/workspace-field.decorator';
+import { WorkspaceIndex } from 'src/engine/twenty-orm/decorators/workspace-index.decorator';
 import { WorkspaceIsDeprecated } from 'src/engine/twenty-orm/decorators/workspace-is-deprecated.decorator';
 import { WorkspaceIsNotAuditLogged } from 'src/engine/twenty-orm/decorators/workspace-is-not-audit-logged.decorator';
 import { WorkspaceIsNullable } from 'src/engine/twenty-orm/decorators/workspace-is-nullable.decorator';
@@ -90,6 +91,7 @@ export class OpportunityWorkspaceEntity extends BaseWorkspaceEntity {
     ],
     defaultValue: "'NEW'",
   })
+  @WorkspaceIndex()
   stage: string;
 
   @WorkspaceField({