Use IterationCadenceID in cadence GraphQL query

What does this MR do and why?

⚠ The changes are strictly internal. Resolves #357461 (closed).

• Use IterationCadenceID over ID in iteration_cadence.query.graphql.

• Fix a typo in the spec filename

  - iteration_breadcumb_spec.js
  + iteration_breadcrumb_spec.js

• Extend the spec coverage for iteration view

  We previously didn't test the behaviors with :iteration_cadences FF enabled. The specs have been added/updated for rigorousness, not due to any change in feature.

Screenshots or screen recordings

None needed.

How to set up and validate locally

We just need to perform cursory checks to ensure that the feature didn't break.

Preparation steps

1. Make sure to disable :iteration_cadences FF first.

   Feature.disable(:iteration_cadences)

2. Visit a group. Navigate to Iteration under Issues via the left sidebar.

   Create a new iteration if none exists.

video walkthrough

Screen_Recording_2022-04-14_at_1.44.03_PM

3. Enable :iteration_cadences again.

   It may take up to 30 seconds to take effect. Go to the group page and then revisit Issues > Iteration via the left menu bar!

   Feature.enable(:iteration_cadences)

Video walkthrough

Screen_Recording_2022-04-14_at_1.48.15_PM

Test drive the feature

1. Check that the cadence list loads

2. Check that you can view, add, update and remove (CRUD) an iteration

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.