Explicitly set workspaceId column as uuid type to ease pg LEFT JOIN (#15430)

Pg scan was redundant because historically the workspaceId was
`varchar`, even though below migration won't change that we had a look
to workspaceId col declaration across the codebase

packages/twenty-server/src/engine/metadata-modules/agent/agent-chat-thread.entity.ts

@@ -20,7 +20,7 @@ export class AgentChatThreadEntity {
   @PrimaryGeneratedColumn('uuid')
   id: string;
 
-  @Column('uuid')
+  @Column({ nullable: false, type: 'uuid' })
   @Index()
   userWorkspaceId: string;
 

packages/twenty-server/src/engine/metadata-modules/index-metadata/index-metadata.entity.ts

@@ -44,7 +44,7 @@ export class IndexMetadataEntity
   @Column({ nullable: false })
   name: string;
 
-  @Column({ nullable: true })
+  @Column({ nullable: false, type: 'uuid' })
   workspaceId: string;
 
   @Column({ nullable: false, type: 'uuid' })