feat(annuaire): Add userRegistry endpoint for research

What does this MR do and why?

Describe in detail what your merge request does and why.

Screenshots or screen recordings

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How to set up and validate locally (or on alpha)

In order to test it with:

• launch the script ./scripts/init-db.js
• launch the app and containers
• Create elastic search indexes by hitting the following URL : http://localhost:3000/api/userRegistry/searchIndex with postman
• Now you have a set of user with jobs and employers ready to be tested

You can test it with frontend:

• In frontend project, go to feat/US176-annuaire-mediateurs
• Access the app and go to http://localhost:4200/annuaire, try to access while logged and not logged
• Play with filters (WIP)

MR acceptance checklist

To be completed by the chosen reviewer.

Quality -

• Confirmed

1. For the code that this change impacts, I believe that the automated tests validate functionality that is highly important to users. If the existing automated tests do not cover this functionality, I have added the necessary additional tests or I have added an issue to describe the automation testing gap and linked it to this MR.
2. I have made sure that the sonar quality coverage is up to standards.
3. I have considered the impact of this change on the front-end, back-end, and database portions of the system where appropriate and applied.
4. I have tested this MR in all supported browsers or determined that this testing is not needed.
5. I have confirmed that this change is backwards compatible across updates (migrate up needs a migrate down), or I have decided that this does not apply.

Performance, reliability and availability

• Confirmed

1. I am confident that this MR does not harm performance, or I have asked a reviewer to help assess the performance impact.
2. I have considered the scalability risk based on future predicted growth.

Documentation

• Confirmed

1. The MR is named after the desired squash commit to feed the changelog linked to the current milestone.
2. I have added/updated documentation (also updated if the changes feature a deprecation) or I have decided that documentation changes are not needed for this MR.

Security

• Confirmed

1. I have confirmed that if this MR does not contains any sensitive informations hidden in the changes.

Deployment

• Confirmed

1. When featured on a self-data project release, i have made sure my app version in the manifest and package.json is incremented and any relative changes to the permissions are clearly written and transmitted to Cozy.