signup: Implement autocomplete for affiliations in custom user registration template

[Samk13]

❤️ Thank you for your contribution!

Description

• Add autocomplete functionality for user affiliations without third-party libraries.
• Gently guide users to select consistent names for the same affiliations especially if user info changes are disabled.
• Fetch suggestions from affiliations API based on user input and display in .
• Cache suggestions for performance and use a debounce mechanism to limit API calls using vanilla JS.
  

Once accepted, after agreeing on where the script should reside and how should be imported e.g invenio-theme, we should update invenio_accounts register_user and user profile template pages.

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• I'm aware of the code of conduct.
• I've created logical separate commits and followed the commit message format.
• I've added relevant test cases.
• I've added relevant documentation.
• I've marked translation strings.
• I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
• I've NOT included third-party code (copy/pasted source code or new dependencies).
  • If you have added third-party code (copy/pasted or new dependencies), please reach out to an architect.

Frontend

• I've followed the CSS/JS and React guidelines.
• I've followed the web accessibility guidelines.
• I've followed the user interface guidelines.

Reminder

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1. You license your contribution under the same terms as the current repository’s license.
2. You agree that you have the right to license your contribution under the current repository’s license.

[Samk13]

Closing this issue in favor of inveniosoftware/invenio-theme#386