fix: format admin url inside forgot pw email (#11509)

### What?
Supersedes https://github.com/payloadcms/payload/pull/11490.

Refactors imports of `formatAdminURL` to import from `payload/shared`
instead of `@payloadcms/ui/shared`. The ui package now imports and
re-exports the function to prevent this from being a breaking change.

### Why?
This makes it easier for other packages/plugins to consume the
`formatAdminURL` function instead of needing to implement their own or
rely on the ui package for the utility.