fix: [UIE-10329] - UpdateDelegationDrawer Follow up

[abailly-akamai]

Description 📝

In #13441 I implemented an infinite query but omitted to handle the case where the user does a Select All, in which case we need to fetch all records.

We're still only fetching the first 25 users when opening the Drawer, so performance isn't affected. It's only if we decide to Select all of them that the expensive query happens, which is a decent workaround.

Changes 🔄

• Add a new onSelectAllClick prop to our Autocomplete (not affecting current usage)
• Fetch all users and select them on SelectAllClick

Scope 🚢

Upon production release, changes in this PR will be visible to:

• All customers
• Some customers (e.g. in Beta or Limited Availability)
• No customers / Not applicable

Preview 📷

Screen.Recording.2026-02-27.at.14.41.04.mov

How to test 🧪

Prerequisites

Have a large parent/child account (many users - ask for being added if not available)

Verification steps

• navigate to /iam/delegations and Click Select ALL in the delegation Autocomplete
• ✅ Confirm all users are fetched
• ✅ Confirm all users are selected
• ✅ Confirm "Deselect ALL" works as intended
• ✅ Select ALL again and Click "Save" and confirm all users we attached to the delegation
• ✅ Confirm no regression on the Autocomplete functionality

Author Checklists

As an Author, to speed up the review process, I considered 🤔

👀 Doing a self review
❔ Our contribution guidelines
🤏 Splitting feature into small PRs
➕ Adding a changeset
🧪 Providing/improving test coverage
🔐 Removing all sensitive information from the code and PR description
🚩 Using a feature flag to protect the release
👣 Providing comprehensive reproduction steps
📑 Providing or updating our documentation
🕛 Scheduling a pair reviewing session
📱 Providing mobile support
♿ Providing accessibility support

• I have read and considered all applicable items listed above.

As an Author, before moving this PR from Draft to Open, I confirmed ✅

• All tests and CI checks are passing
• TypeScript compilation succeeded without errors
• Code passes all linting rules

[aaleksee-akamai]

nit: if you clear an input, then start typing - first, you'll see you have no options and only then a loading spinner and later a result

[aaleksee-akamai]

I like this approach, looks good!