Migrate angle icon to chevron for iteration breadcrumb

What does this MR do and why?

Migrate the angle icon to the chevron counterpart in ee/app/assets/javascripts/iterations/components/iteration_breadcrumb.vue

Closes #362787 (closed)

Screenshots or screen recordings

Screenshots

Before	After

How to set up and validate locally

1. Visit any group with Iterations (requires license)
2. Go to Issues > Iterations
3. On the Iterations list, click Edit cadence within the ellipses icon of a specific iteration. The details page/view opens.

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.