Use graphQL boards for project boards and fix associated rspecs [RUN AS-IF-FOSS]

What does this MR do?

Issue #248908 (closed)

backend and test changes

1. enables :graphql_board_lists FF for project boards (the FF's been enabled for group boards / the FF itself is turned off by default).

2. fixes a various boards and boards sidebar related feature specs to work with the graphql-based boards code.

   • the fixes are mostly about css selector related fixes and adding wait_for_requests to wait for graphql requests.
   • for the features not yet implemented for or deprecated in the graphql-based boards, I've created follow up issues to track them after skipping the examples (xit) or stubbing :graphql_board_lists as false.

frontend changes

1. weight field should not be included when creating a new issue via graphql in CE. Weight is a GitLab Premium feature.

2. moveItem vuex action should forward its payload to moveIssue action.

---

⚠ :graphql_board_lists is still stubbed as false in the following specs:

(detailed in each commit message too)

specs	reason
spec/features/boards/sidebar_spec.rb spec/features/boards/sidebar_subscription_spec.rb spec/features/boards/sidebar_time_tracking_spec.rb spec/features/boards/sidebar_milestones_spec.rb spec/features/boards/sidebar_labels_spec.rb spec/features/boards/sidebar_due_date_spec.rb spec/features/boards/sidebar_assignee_spec.rb	These specs have been flaky in CI and I want to leave them for a few days to see if the issue's been resolved (#323325 (closed))
spec/features/boards/sub_group_project_spec.rb ee/spec/features/issues/filtered_search/filter_issues_by_iteration_spec.rb:82 multi_select_spec.rb	Features have not been implemented in graphql-based boards
add_issues_modal_spec.rb (ee and ce)	these are being deprecated behind a feature flag :add_issue_button

---

Follow-up issues

• #323446 (closed)
• #324290 (closed)

Screenshots (strongly suggested)

The easiest way to distinguish a graphql-based boards from a classic boards is by checking out the sidebar. In the graphql-based boards, the sidebar is non-collapsible.

Project Boards - Before	Project Boards - After

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
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