(Part 6) FE multiple approval rules - fallback rule & mr edit

What does this MR do?

• Updates the project settings components to show a "Fallback Rule" based on this requirement change.
• Adds the components and store for the MR edit page.

To run locally, enable the approval_rules and multiple_approval_rules flag.

MR Instructions!

This points to Part 5 https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9432

• When Part 5 is merged, point this to the feature branch https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9001

What's going to come in later MR's?

• GitLab Starter single rule functionality.

What are the relevant issue numbers?

Part of #1979 (closed)

Part of https://gitlab.com/gitlab-org/gitlab-ee/issues/8350 (FE)

Screenshots

Old Project Settings (current feature branch)	New Project Settings

MR Edit (with project rules)	MR Edit (with no rules and override)	MR Edit demo

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• EE specific content should be in the top level /ee folder
• For a paid feature, have we considered GitLab.com plans, how it works for groups, and is there a design for promoting it to users who aren't on the correct plan?
• Security reports checked/validated by reviewer