Fix various proposal picker issues when there are thousands of proposals

[alecslupu]

🎩 What? Why?

Fixing 2 related issues in the proposal picker.

📌 Related Issues

Link your PR to an issue

• Fixes Searching proposals in proposal picker raises exception #8555
• Fixes Proposal picker does not select items when AJAX search is used #8557

Testing

Please check the associated tickets to see both use cases.

📋 Checklist

🚨 Please review the guidelines for contributing to this repository.

• ❓ CONSIDER adding a unit test if your PR resolves an issue.
• ✔️ DO check open PR's to avoid duplicates.
• ✔️ DO keep pull requests small so they can be easily reviewed.
• ✔️ DO build locally before pushing.
• ✔️ DO make sure tests pass.
• ✔️ DO make sure any new changes are documented in docs/.
• ✔️ DO add and modify seeds if necessary.
• ✔️ DO add CHANGELOG upgrade notes if required.
• ✔️ DO add to GraphQL API if there are new public fields.
• ✔️ DO add link to MetaDecidim if it's a new feature.
• ❌AVOID breaking the continuous integration build.
• ❌AVOID making significant changes to the overall architecture.

♥️ Thank you!

[andreslucena]

Thanks for the PR @alecslupu 👍🏽 👍🏽

[andreslucena]

As this is a fix, could you make a backport to v0.25-stable @alecslupu 🙏🏽?