Auth Web and other UIs: use common Business Search composable

In #16621, a business search component was written, based on a similar component in Create UI and Edit UI. In fact, a similar component also exists in MHR and in Business Search. Some are written in Class API and some are written in Composition API.

Ideally, there would be 1 common business search component, written as a composable, that all UIs could import once they are upgraded to Vue3.

- [ ] create reusable composable (from Business Search?)
- needs to support various search parameters
- needs to support various business search URLs
- needs to support various business search API keys
- needs to supoprt various account IDs
- probably needs slot(s) to display results (list) in a flexible manner
- may need props (or equivalent) to display messages in a flexible manner
- see also extra functionality in Auth Web for disabling businesses that are already affiliated
- what about the Business Search service (API code)?
- add more here as needed...
- [ ] import and use it in Auth Web
- [ ] import and use it in Create UI
- [ ] import and use it in Edit UI
- [ ] import and use it in MHR?

Refs:
https://github.com/bcgov/sbc-auth/pull/2365#discussion_r1235819821
https://github.com/bcgov/sbc-auth/pull/2365#discussion_r1235945743

Compare the existing Business Search components in Create UI, Edit UI, MHR, Business Search, and Auth Web, starting with the referenced discussion in bcgov/sbc-auth pull request 2365. Define the shared composable's supported parameters, URLs, API keys, account IDs, result slots, messages, and Auth Web's affiliation behavior before implementation. Done means the agreed composable is used by the applicable upgraded UIs and its behavior is covered by the relevant tests.

Written by the indexing model from the issue text.