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
- [x] User profile - `/<username>`
- [x] Environments dashboard - `/-/operations/environments`, `ee/app/views/operations/environments.html.haml`
- [x] Operations dashboard `/-/operations`, `ee/app/views/operations/index.html.haml`
- [x] Enter Admin Mode - `app/views/admin/sessions/new.html.haml`
- [x] Enter 2FA for Admin Mode - `app/views/admin/sessions/two_factor.html.haml`
- [x] Jira - Create branch - `app/views/jira_connect/branches/new.html.haml`
- [x] Terms - `app/views/layouts/terms.html.haml` _(Layout! So probably multiple pages here - no need for breadcrumbs)_
- [x] Search - `app/views/search/show.html.haml`
- [x] Discover Premium & Ultimate - `ee/app/views/groups/feature_discovery_moments/advanced_features_dashboard.html.haml`
- [x] 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.
## Design specs
TBD
epic