12679 non whitespace validator

[mishalsheza]

[#12679]Copying feedback session: Name for copied session should not be whitespace

Fixes #12679

Outline of Solution

Added a custom validator to the email field to ensure it does not contain only whitespace.

teammates/src/web/app/pages-help/session-links-recovery/session-links-recovery-page.component.ts

Custom Validator (noWhitespaceValidator): This validator checks if the input contains only whitespace and returns an error if it does.

Form Group Initialization: Updated the form group initialization in both ngOnInit and resetFormGroups to include the custom validator for the email field.

Error Handling: Ensure that the error messages are handled appropriately in the UI if the validator detects a whitespace-only value.

This approach ensures that any whitespace-only values for the email field are effectively handled both on the client side and before submission.

[github-actions]

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