Add breadcrumbs to all pages in GitLab that need breadcrumbs

Proposal

Catalog all the pages missing breadcrumbs and begin to convert them.

List of pages

• User profile - /<username>
• Environments dashboard - /-/operations/environments, ee/app/views/operations/environments.html.haml
• Operations dashboard /-/operations, ee/app/views/operations/index.html.haml
• Enter Admin Mode - app/views/admin/sessions/new.html.haml
• Enter 2FA for Admin Mode - app/views/admin/sessions/two_factor.html.haml
• Jira - Create branch - app/views/jira_connect/branches/new.html.haml
• Terms - app/views/layouts/terms.html.haml (Layout! So probably multiple pages here.)
• Search - app/views/search/show.html.haml
• Discover Premium & Ultimate - ee/app/views/groups/feature_discovery_moments/advanced_features_dashboard.html.haml
• GitLab for Slack - ee/app/views/profiles/slacks/edit.html.haml
• more?*

*: Any page that uses the page.html.haml layout and doesn't set @hide_breadcrumbs = true does have them. We still need to check which pages use a different layout, like all out sign-in/up pages, for example.

List of false positives searching for @hide_breadcrumbs

• New Group - app/views/groups/new.html.haml: Classic Haml breadcrumbs are disabled here because breadcrumbs are done within Vue component using GlBreadcrumb.
• New Project - app/views/projects/new.html.haml: Same as above.