change: [M3-10449] - Enhance Linode alerts input validation messages behavior

[pmakode-akamai]

Description 📝

There is an existing issue with how validation messages are handled in the Legacy Alerts form using Formik. Currently, validation messages only appear when the form is submitted, which is not an ideal user experience.

This issue is not limited to Legacy Alerts; similar behavior can be observed in few other areas such as the Domain Edit Drawer. However, as part of the Linode-ACLP Integration and to improve the UX, we should enhance the validation message behavior for Legacy Alerts.

The validation messages behavior should be updated to display:

• On blur of individual input fields
• Or when the form is submitted

Changes 🔄

• Added support for displaying client-side validation errors on blur for input fields
• Updated alertsSchema to mark numeric input fields as required when empty
• Improved validation messages for better clarity and user feedback

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

Target release date 🗓️

N/A

Preview 📷

Before	After
Screen.Recording.2025-08-14.at.10.11.32.PM.mov	Screen.Recording.2025-08-14.at.10.14.50.PM.mov

How to test 🧪

Verification steps

• Verify that the Linode Alerts edit form functions correctly without regressions
• Confirm that client-side validation behaves as expected:
  • Errors display on blur for invalid or empty numeric fields
  • Appropriate validation messages appear based on the updated schema
• Ensure all tests pass

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

[dmcintyr-akamai]

Fixes the reported issue in alerts form. Maybe out of scope of this pr, but would be nice if the appearance of an input error disabled the Save button
Also would also be nice if there was a error summary, preferably at the bottom of the page, so that i know why the Save button is disabled. On some really long forms, the error msg appears above the fold when i scroll down to the save button.

[linode-gh-bot]

Cloud Manager UI test results

🎉 724 passing tests on test run #4 ↗︎

❌ Failing	✅ Passing	↪️ Skipped	🕐 Duration
0 Failing	724 Passing	4 Skipped	122m 58s

[coliu-akamai]

✅ functionality looks good - didn't see regressions
✅ client side validation looks good

thanks @pmakode-akamai!