change: hide placeholder once a value is selected in Autocomplete multi-select mode

[harsh-akamai]

Description 📝

MUI v7 Autocomplete shows placeholder even after options are selected in multi-select mode. This PR adds logic to hide the placeholder when at least one option is selected when multi-select is enabled.

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 📷

Before	After

How to test 🧪

Reproduction steps

• Navigate to an Autocomplete based component that has multi-select enabled (http://localhost:3000/firewalls/create)
• Select an option and you will be able to see the placeholder still persists

Verification steps

• Observe that the placeholder no more exists when an option is selected in multi-select mode

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

[linode-gh-bot]

Cloud Manager UI test results

🎉 865 passing tests on test run #1 ↗︎

❌ Failing	✅ Passing	↪️ Skipped	🕐 Duration
0 Failing	865 Passing	11 Skipped	40m 8s